| 1. |
- Adnan, Md Mohsinur Rahman, et al.
(författare)
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Anisotropic Beer-Lambert law in β - Ga2 O3 : Polarization-dependent absorption and photoresponsivity spectra
- 2024
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Ingår i: Physical Review Applied. - 2331-7019. ; 21:5
-
Tidskriftsartikel (refereegranskat)abstract
- Due to its low symmetry, β-Ga2O3 exhibits a strongly anisotropic optical response. As a result, the absorption spectra change with the polarization state of the incoming photons. To understand this phenomenon, here we calculate the complete electromagnetic wave equation solutions as a function of linear polarization angle and photon energy for β-Ga2O3 using its previously measured complex dielectric function tensor. The significant off-diagonal terms in this tensor can result in a nonexponential decay in the photon flux, indicating that the Beer-Lambert law is not generally valid in this anisotropic material. However, for above-band-gap spectral regions that depend on crystallographic orientations [>5.8 eV (001-plane) and >5.2 eV (010-plane)], an effective absorption coefficient closely approximates the photon flux decay with depth. On the other hand, near the optical absorption edge [4.9-5.8 eV (001-plane) and 4.65-5.2 eV (010-plane)], the photon flux decay exhibits a sum of two exponential decays, such that two effective absorption coefficients are necessary to model the loss behavior versus the absorption depth. This behavior manifests from the presence of dichroism in β-Ga2O3. A single effective absorption coefficient can only be recovered for this energy range by augmenting the isotropic Beer-Lambert law with a critical penetration depth and polarization dependence. Using these results, we calculate the polarization-dependent photoresponsivity spectra for light polarized along different crystallographic directions.
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| 2. |
- Alarcon, Alvaro, 1991-, et al.
(författare)
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Few-Mode-Fiber Technology Fine-tunes Losses in Quantum Communication Systems
- 2021
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Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 16:3
-
Tidskriftsartikel (refereegranskat)abstract
- A natural choice for quantum communication is to use the relative phase between two paths of a single photon for information encoding. This method was nevertheless quickly identified as impractical over long distances, and thus a modification based on single-photon time bins has become widely adopted. It, how-ever, introduces a fundamental loss, which increases with the dimension and limits its application over long distances. Here solve this long-standing hurdle by using a few-mode-fiber space-division-multiplexing platform working with orbital-angular-momentum modes. In our scheme, we maintain the practicability provided by the time-bin scheme, while the quantum states are transmitted through a few-mode fiber in a configuration that does not introduce postselection losses. We experimentally demonstrate our proposal by successfully transmitting phase-encoded single-photon states for quantum cryptography over 500 m of few-mode fiber, showing the feasibility of our scheme.
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| 3. |
- Anghel, D. V., et al.
(författare)
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Cold-Electron Bolometer as a 1-cm-Wavelength Photon Counter
- 2020
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Ingår i: Physical Review Applied. - 2331-7019. ; 13:2
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate theoretically the possibility of using the cold-electron bolometer (CEB) as a counter for 1-cm-wavelength (30-GHz) photons. To reduce the flux of photons from the environment that interact with the detector, the bath temperature is assumed to be below 50 mK. At such temperatures, the time interval between two subsequent photons of 30 GHz that hit the detector is more than 100 h, on average, for a frequency window of 1 MHz. Such temperatures allow the observation of the physically significant photons produced in rare events, such as axion conversion (or Primakoff conversion) in a magnetic field. We present the general formalism for the detector's response and noise, together with numerical calculations for proper experimental setups. We observe that the current-biased regime is favorable due to lower noise and allows for photon counting at least below 50 mK. For the experimental setups investigated here, the voltage-biased CEBs may also work as photon counters but with less accuracy and, eventually, may require smaller volumes of the normal-metal island.
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| 4. |
- Arora, Monika, et al.
(författare)
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Magnetic Damping in Polycrystalline Thin-Film Fe-V Alloys
- 2021
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Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 15:5
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the magnetic damping properties of polycrystalline Fe-V alloy thin films that are deposited at room temperature. By varying the concentration of V in the alloy, the saturation magnetization can be adjusted from that of Fe to near zero. We show that exceptionally low values of the damping parameter can be maintained over the majority of this range, with a minimum damping at approximately 15%-20% V concentration. Such a minimum is qualitatively reproduced with ab initio calculations of the damping parameter, although at a concentration closer to 10% V. The measured intrinsic damping has a minimum value of (1.53 +/- 0.08) x 10-3, which is approximately a factor of 3 higher than our calculated value of 0.48 x 10-3. From first-principles theory, we outline the factors that are mainly responsible for the trend of the damping parameter in these alloys. In particular, the band structure and resulting damping mechanism is shown to change at V concentrations greater than approximately 35% V content.
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| 5. |
- Aurino, Pier Paolo, 1985, et al.
(författare)
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Retention of Electronic Conductivity in LaAlO3/SrTiO3 Nanostructures Using a SrCuO2 Capping Layer
- 2016
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Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 6:2
-
Tidskriftsartikel (refereegranskat)abstract
- The interface between two wide band-gap insulators, LaAlO3 and SrTiO3 (LAO/STO) offers a unique playground to study the interplay and competitions between different ordering phenomena in a strongly correlated two- dimensional electron gas. Recent studies of the LAO/STO interface reveal the inhomogeneous nature of the 2DEG that strongly influences electrical-transport properties. Nanowires needed in future applications may be adversely affected, and our aim is, thus, to produce a more homogeneous electron gas. In this work, we demonstrate that nanostructures fabricated in the quasi-2DEG at the LaAlO3/SrTiO3 interface, capped with a SrCuO2 layer, retain their electrical resistivity and mobility independent of the structure size, ranging from 100 nm to 30 mu m. This is in contrast to noncapped LAO/STO structures, where the room-temperature electrical resistivity significantly increases when the structure size becomes smaller than 1 mu m. High-resolution intermodulation electrostatic force microscopy reveals an inhomogeneous surface potential with "puddles" of a characteristic size of 130 nm in the noncapped samples and a more uniform surface potential with a larger characteristic size of the puddles in the capped samples. In addition, capped structures show superconductivity below 200 mK and nonlinear currentvoltage characteristics with a clear critical current observed up to 700 mK. Our findings shed light on the complicated nature of the 2DEG at the LAO/STO interface and may also be used for the design of electronic devices.
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| 6. |
- Baasch, Thierry, et al.
(författare)
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Gap Distance Between Pearl Chains in Acoustic Manipulation
- 2022
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Ingår i: Physical Review Applied. - 2331-7019. ; 18:1
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Tidskriftsartikel (refereegranskat)abstract
- We present a theory to compute the stable gap (interparticle) distance between particle chains collected in the pressure node of an acoustic standing wave. The primary and secondary acoustic radiation forces are the two competing forces that act on the particles during the particle chain formation. The stable equilibrium distance between two chains is reached when both forces are in balance. Most interestingly, the density scattering coefficient appears to the second power in the theoretical prediction of the gap distance, indicating that the particle-chain formation occurs for both particles heavier than the surrounding medium and, notably, also for buoyant particles. Experimentally, the gap distance is evaluated for several different media and particle material combinations and the particle-chain formation is observed for both buoyantparticles and particles heavier than the surrounding medium. The theory agrees well with experiments in the cases where the material properties of the medium and the particles are well known.
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| 7. |
- Baghdadi, Reza, 1984, et al.
(författare)
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Fabricating Nanogaps in YBa2Cu3O7-delta for Hybrid Proximity-Based Josephson Junctions
- 2015
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Ingår i: Physical Review Applied. - 2331-7019. ; 4:1
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Tidskriftsartikel (refereegranskat)abstract
- The advances of nanotechnologies applied to high-critical-temperature superconductors (HTSs) have recently given a huge boost to the field, opening new prospectives for their integration in hybrid devices. The feasibility of this research goes through the realization of HTS nanogaps with superconductive properties close to the as-grown bulk material at the nanoscale. Here we present a fabrication approach allowing the realization of YBa2Cu3O7-delta (YBCO) nanogaps with dimensions as small as 35 nm. To assess the quality of the nanogaps, we measure, before and after an ozone treatment, the current-voltage characteristics and the resistance versus temperature of YBCO nanowires with various widths and lengths, fabricated by using different lithographic processes. The analysis of the superconducting transition with a thermally activated vortex-entry model allows us to determine the maximum damage the nanowires undergo during the patterning which relates to the upper bound for the dimension of the nanogap. We find that the effective width of the nanogap is of the order of 100 nm at the superconducting transition temperature while retaining the geometrical value of about 35 nm at lower temperatures. The feasibility of the nanogaps for hybrid Josephson devices is demonstrated by bridging them with thin Au films. We detect a Josephson coupling up to 85 K with an almost ideal magnetic-field response of the Josephson current. These results pave the way for the realization of complex hybrid devices, where tiny HTS nanogaps can be instrumental to study the Josephson effect through barriers such as topological insulators or graphene.
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| 8. |
- Behera, Nilamani, et al.
(författare)
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Energy-Efficient W100-xTax/ Co-Fe-B/MgO Spin Hall Nano-Oscillators
- 2022
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Ingår i: Physical Review Applied. - 2331-7019. ; 18:2
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Tidskriftsartikel (refereegranskat)abstract
- We investigate a W-Ta alloying route to reduce the auto-oscillation threshold current densities and the power consumption of nanoconstriction based spin Hall nano-oscillators. Using spin-torque ferromagnetic resonance measurements on microbars of W100-xTax(5 nm)/Co-Fe-B(t)/MgO stacks with t=1.4, 1.8, and 2.0 nm, we measure a substantial improvement in both the spin-orbit torque efficiency and the spin Hall conductivity. We demonstrate a 34% reduction in auto-oscillation threshold current density, which translates into a 64% reduction in power consumption as compared with pure W-based spin Hall nano-oscillators. Our work demonstrates the promising aspects of W-Ta alloying for the energy-efficient operation of emerging spintronic devices.
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| 9. |
- Bejanin, J. H., et al.
(författare)
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Three-Dimensional Wiring for Extensible Quantum Computing: The Quantum Socket
- 2016
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Ingår i: Physical Review Applied. - 2331-7019. ; 6:4
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Tidskriftsartikel (refereegranskat)abstract
- Quantum computing architectures are on the verge of scalability, a key requirement for the implementation of a universal quantum computer. The next stage in this quest is the realization of quantum error-correction codes, which will mitigate the impact of faulty quantum information on a quantum computer. Architectures with ten or more quantum bits (qubits) have been realized using trapped ions and superconducting circuits. While these implementations are potentially scalable, true scalability will require systems engineering to combine quantum and classical hardware. One technology demanding imminent efforts is the realization of a suitable wiring method for the control and the measurement of a large number of qubits. In this work, we introduce an interconnect solution for solid-state qubits: the quantum socket. The quantum socket fully exploits the third dimension to connect classical electronics to qubits with higher density and better performance than two-dimensional methods based on wire bonding. The quantum socket is based on spring-mounted microwires-the three-dimensional wires-that push directly on a microfabricated chip, making electrical contact. A small wire cross section (approximately 1 mm), nearly nonmagnetic components, and functionality at low temperatures make the quantum socket ideal for operating solid-state qubits. The wires have a coaxial geometry and operate over a frequency range from dc to 8 GHz, with a contact resistance of approximately 150 m Omega, an impedance mismatch of approximately 10 Omega, and minimal cross talk. As a proof of principle, we fabricate and use a quantum socket to measure high-quality superconducting resonators at a temperature of approximately 10 mK. Quantum error-correction codes such as the surface code will largely benefit from the quantum socket, which will make it possible to address qubits located on a two-dimensional lattice. The present implementation of the socket could be readily extended to accommodate a quantum processor with a (10 x 10)-qubit lattice, which would allow for the realization of a simple quantum memory.
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| 10. |
- Bengtsson, Andreas, 1991, et al.
(författare)
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Improved Success Probability with Greater Circuit Depth for the Quantum Approximate Optimization Algorithm
- 2020
-
Ingår i: Physical Review Applied. - 2331-7019. ; 14:3
-
Tidskriftsartikel (refereegranskat)abstract
- Present-day, noisy, small or intermediate-scale quantum processors-although far from fault tolerant-support the execution of heuristic quantum algorithms, which might enable a quantum advantage, for example, when applied to combinatorial optimization problems. On small-scale quantum processors, validations of such algorithms serve as important technology demonstrators. We implement the quantum approximate optimization algorithm on our hardware platform, consisting of two superconducting transmon qubits and one parametrically modulated coupler. We solve small instances of the NP (nondeterministic polynomial time)-complete exact-cover problem, with 96.6% success probability, by iterating the algorithm up to level two.
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| 11. |
- Biznárová, Janka, 1995, et al.
(författare)
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Intermodulation spectroscopy and the nonlinear response of two-level systems in superconducting coplanar-waveguide resonators
- 2024
-
Ingår i: Physical Review Applied. - : American Physical Society (APS). - 2331-7019. ; 22:1
-
Tidskriftsartikel (refereegranskat)abstract
- Two-level system (TLS) loss typically limits the coherence of superconducting quantum circuits. The loss induced by TLS defects is nonlinear, resulting in quality factors with a strong dependence on the circulating microwave power. We observe frequency mixing due to this nonlinearity by applying a two-tone drive to a coplanar waveguide resonator and measuring the intermodulation products using a multifrequency lock-in technique. This intermodulation spectroscopy method provides an efficient approach to characterizing TLS loss in superconducting circuits. Using harmonic balance reconstruction, we recover the nonlinear parameters of the device-TLS interaction, which are in good agreement with the standard tunneling model for TLSs.
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| 12. |
- Bodé, William N., et al.
(författare)
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Determination of the Complex-Valued Elastic Moduli of Polymers by Electrical-Impedance Spectroscopy for Ultrasound Applications
- 2022
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Ingår i: Physical Review Applied. - 2331-7019. ; 18:6
-
Tidskriftsartikel (refereegranskat)abstract
- A method is presented for the determination of complex-valued compression and shear elastic moduli of polymers for ultrasound applications. The resulting values, which are scarcely reported in the literature, are found with uncertainties typically around 1% (real part) and 6% (imaginary part). The method involves a setup consisting of a cm-radius, mm-thick polymer ring glued concentrically to a disk-shaped piezoelectric transducer. The ultrasound electrical-impedance spectrum of the transducer is computed numerically and fitted to measured values as an inverse problem in a wide frequency range, typically from 500 Hz to 5 MHz, both on and off resonance. The method is validated experimentally by ultrasonic through transmission around 1.9 MHz. The method is low cost, not limited to specific geometries and crystal symmetries, and, given the developed software, easy to execute. The method has no obvious frequency limitations before severe attenuation sets in above 100 MHz.
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| 13. |
- Booker, Ian Don, et al.
(författare)
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Oxidation-induced deep levels in n- and p-type 4H- and 6H-SiC and their influence on carrier lifetime
- 2016
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Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 6:1, s. 1-15
-
Tidskriftsartikel (refereegranskat)abstract
- We present a complete analysis of the electron- and hole-capture and -emission processes of the deep levels ON1, ON2a, and ON2b in 4H-SiC and their 6H-SiC counterparts OS1a and OS1b through OS3a and OS3b, which are produced by lifetime enhancement oxidation or implantation and annealing techniques. The modeling is based on a simultaneous numerical fitting of multiple high-resolution capacitance deep-level transient spectroscopy spectra measured with different filling-pulse lengths in n- and p-type material. All defects are found to be double-donor-type positive-U two-level defects with very small hole-capture cross sections, making them recombination centers of low efficiency, in accordance with minority-carrier-lifetime measurements. Their behavior as trapping and weak recombination centers, their large concentrations resulting from the lifetime enhancement oxidations, and their high thermal stability, however, make it advisable to minimize their presence in active regions of devices, for example, the base layer of bipolar junction transistors.
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| 14. |
- Borgani, Riccardo, et al.
(författare)
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Background-Force Compensation in Dynamic Atomic Force Microscopy
- 2017
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Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 7:6
-
Tidskriftsartikel (refereegranskat)abstract
- Background forces are linear long-range interactions of the cantilever body with its surroundings that must be compensated for in order to reveal tip-surface force, the quantity of interest for determining material properties in atomic force microscopy. We provide a mathematical derivation of a method to compensate for background forces, apply it to experimental data, and discuss how to include background forces in simulation. Our method, based on linear-response theory in the frequency domain, provides a general way of measuring and compensating for any background force and it can be readily applied to different force reconstruction methods in dynamic AFM.
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| 15. |
- Borgani, Riccardo, et al.
(författare)
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Fast Multifrequency Measurement of Nonlinear Conductance
- 2019
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Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 11:4
-
Tidskriftsartikel (refereegranskat)abstract
- We describe a phase-coherent multifrequency lock-in measurement technique that uses the inverse Fourier transform to reconstruct the nonlinear current-voltage characteristic of a nanoscale junction. The method provides separation of the galvanic and displacement currents in the junction and easy cancellation of the parasitic displacement current from the measurement leads. These two features allow us to overcome traditional limitations imposed by the low conductance of the junction and the high capacitance of the leads, thus providing an increase in measurement speed of several orders of magnitude. We demonstrate the method in the context of conductive atomic force microscopy, acquiring current-voltage characteristics at every pixel while scanning at standard imaging speed.
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| 16. |
- Bulancea Lindvall, Oscar, et al.
(författare)
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Isotope-Purification-Induced Reduction of Spin-Relaxation and Spin-Coherence Times in Semiconductors
- 2023
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Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 19:6
-
Tidskriftsartikel (refereegranskat)abstract
- Paramagnetic defects and nuclear spins are often the major sources of decoherence and spin relaxation in solid-state qubits realized by optically addressable point defect spins in semiconductors. It is commonly accepted that a high degree of depletion of nuclear spins can enhance the coherence time by reducing magnetic noise. Here we show that the isotope purification beyond a certain optimal level can become contraproductive when both electron and nuclear spins are present in the vicinity of the qubits, particularly for half-spin systems. Using state-of-the-art numerical tools and considering the silicon-vacancy qubit in various spin environments, we demonstrate that the coupling of the spin-3/2 qubit to a spin bath of spin-1/2 point defects in the lattice can be significantly enhanced by isotope purification. The enhanced coupling shortens the spin-relaxation time that in turn may limit the coherence time of spin qubits. Our results can be generalized to triplet point defect qubits, such as the nitrogen-vacancy center in diamond and the divacancy in silicon carbide.
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| 17. |
- Bulancea Lindvall, Oscar, et al.
(författare)
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Low-Field Microwave-Free Magnetometry Using the Dipolar Spin Relaxation of Quartet Spin States in Silicon Carbide
- 2023
-
Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 19:3
-
Tidskriftsartikel (refereegranskat)abstract
- Paramagnetic defects and nuclear spins are the major sources of magnetic-field-dependent spin relaxation in point-defect quantum bits. The detection of related optical signals has led to the development of advanced relaxometry applications with high spatial resolution. The nearly degenerate quartet ground state of the silicon-vacancy qubit in silicon carbide (SiC) is of special interest in this respect, as it gives rise to relaxation-rate extrema at vanishing magnetic field values and emits in the first near-infrared transmission window of biological tissues, providing an opportunity for the development of sensing applications for medicine and biology. However, the relaxation dynamics of the silicon-vacancy center in SiC have not yet been fully explored. In this paper, we present results from a comprehensive theoretical investigation of the dipolar spin relaxation of the quartet spin states in various local spin environments. We discuss the underlying physics and quantify the magnetic field and spin-bath-dependent relaxation time T1. Using these findings, we demonstrate that the silicon-vacancy qubit in SiC can implement microwave-free low-magnetic-field quantum sensors of great potential.
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| 18. |
- Bylander, Jonas, 1978
(författare)
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Z-Gate Operation on a Superconducting Flux Qubit via its Readout SQUID
- 2015
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Ingår i: Physical Review Applied. - 2331-7019. ; 3:3, s. 034004-
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Tidskriftsartikel (refereegranskat)abstract
- Detuning a superconducting qubit from its rotating frame is one means to implement a Z-gate operation. In this work, we implement a Z gate by pulsing a current through the qubit’s readout dc SQUID. While the dc SQUID acts as a magnetic flux sensor for qubit readout, we in turn may use it as a flux actuator with tunable strength to impose a qubit frequency shift. Using this approach, we demonstrate Ramsey-type free-induction experiments with time constants as long as 280 ns and rotation frequencies as high as 1.4 GHz. We experimentally demonstrate an inferred Z-gate fidelity of approximately 90%, limited largely by the bandwidth of our system. In the absence of this limitation, we argue that the inferred fidelity may be improved to as high as 99%.
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| 19. |
- Cattaneo, Roger, et al.
(författare)
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Superconducting Terahertz Sources with 12% Power Efficiency
- 2021
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Ingår i: Physical Review Applied. - 2331-7019. ; 16:6
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Tidskriftsartikel (refereegranskat)abstract
- Low power efficiency is one of the main problems of terahertz (THz) sources, colloquially known as “the THz gap.” In this work we present prototypes of THz devices based on whisker crystals of a high-temperature superconductor Bi2Sr2CaCu2O8+δ with a record high-radiation power efficiency of 12% at a frequency of approximately 4 THz. We employ various on- and off-chip detection techniques and, in particular, use the radiative cooling phenomenon for accurate evaluation of the emission power. We conclude that such devices can be used for creation of tunable, monochromatic, cw, compact, and power-efficient THz sources.
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| 20. |
- Chang, C. W. Sandbo, et al.
(författare)
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Generating Multimode Entangled Microwaves with a Superconducting Parametric Cavity
- 2018
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Ingår i: Physical Review Applied. - 2331-7019. ; 10:4
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the generation of multimode entangled states of propagating microwaves. The entangled states are generated by our parametrically pumping a multimode superconducting cavity. By combining different pump frequencies, applied simultaneously to the device, we can produce different entanglement structures in a programable fashion. The Gaussian output states are fully characterized by our measuring the full covariance matrices of the modes. The covariance matrices are absolutely calibrated by our using an in situ microwave calibration source, a shot-noise tunnel junction. Applying a variety of entanglement measures, we demonstrate both full inseparability and genuine tripartite entanglement of the states. Our method is easily extensible to more modes.
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| 21. |
- Chen, K., et al.
(författare)
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Observation of a Chirality-Induced Exchange-Bias Effect
- 2019
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Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 12:2
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Tidskriftsartikel (refereegranskat)abstract
- Chiral magnetism that manifests in the existence of skyrmions or chiral domain walls offers an alternative way for creating anisotropies in magnetic materials that might have large potential for application in future spintronic devices. Here we show experimental evidence for an alternative type of in-plane exchange-bias effect present at room temperature that is created from a chiral 90 degrees domain wall at the interface of a ferrimagnetic-ferromagnetic Dy-Co/Ni-Fe bilayer system. The chiral interfacial domain wall forms due to the exchange coupling of Ni-Fe and Dy-Co at the interface and the presence of Dzyaloshinskii-Moriya interaction in the Dy-Co layer. As a consequence of the preferred chirality of the interfacial domain wall, the sign of the exchange-bias effect can be reversed by changing the perpendicular orientation of the Dy-Co magnetization. The chirality-created tunable exchange bias in Dy-Co/Ni-Fe is very robust against high in-plane magnetic fields (mu H-0 <= 6 T) and does not show any aging effects. Therefore, it overcomes the limitations of conventional exchange-bias systems.
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| 22. |
- Chen, X, et al.
(författare)
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Modulated Photoluminescence Mapping of Long-Wavelength Infrared InAs / GaSb Type-II Superlattice: In-Plane Optoelectronic Uniformity
- 2021
-
Ingår i: Physical Review Applied. - 2331-7019. ; 15:4
-
Tidskriftsartikel (refereegranskat)abstract
- In-plane uniformity of narrow-gap semiconductor InAs/GaSb type-II superlattice (T2SL) wafer is a crucial yet hard-to-evaluate prerequisite for high-performance long-wavelength infrared optoelectronic device applications of, e.g., focal-plane-array (FPA) photodetectors. In this work, we report a modulated photoluminescence-mapping (PL-mapping) study of InAs/GaSb T2SL in long-wavelength infrared range with a spatial resolution of a typical FPA-pixel scale. Spatial distributions are analyzed of PL-peak energy, linewidth, and integral intensity, which indicate a high in-plane uniformity of effective band gap but a considerable fluctuation of radiative recombination. The in-plane distributions of effective carrier lifetime and Shockley-Read-Hall defect concentration are evaluated, with the aid of a model that takes into account the pumping power dependence of the PL integral intensity. The results reveal a considerable in-plane nonuniformity of the optoelectronic response that may restrict the performance of the derivative FPA photodetector, and indicate the modulated PL mapping of a good pathway particularly for uniformity analysis of long-wavelength infrared FPA semiconductors.
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| 23. |
- Dashti, Nastaran, 1988, et al.
(författare)
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Probing charge- and heat-current noise by frequency-dependent fluctuations in temperature and potential
- 2018
-
Ingår i: Physical Review Applied. - 2331-7019. ; 10:2
-
Tidskriftsartikel (refereegranskat)abstract
- The energetic properties of electron transport in mesoscopic and nanoscale conductors are of considerable interest at present. Here, we theoretically investigate the possibility of probing charge- and heat-current fluctuations as well as their mixed correlations via the temperature and electrochemical potential fluctuations of a probe coupled to the conductor. Our particular interest is devoted to the charge and energy noise stemming from time-dependently-driven nanoelectronic systems designed for the controlled emission of single electrons, even though our setup is appropriate for more general ac-driving schemes. We employ a Boltzmann-Langevin approach in order to relate the bare charge- and energy-current fluctuations emitted from the electron source to frequency-dependent electrochemical potential and temperature fluctuations, which the former induce in the probe. We apply our findings to the prominent example of an on-demand single-electron source, realized by a driven mesoscopic capacitor in the quantum Hall regime. We show that neither the background fluctuations of the probe in the absence of the working source, nor the fluctuations induced by the probe hinder the access to the sought-after direct source noise for a large range of parameters.
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| 24. |
- Dvornik, Mykola, et al.
(författare)
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Origin of Magnetization Auto-Oscillations in Constriction-Based Spin Hall Nano-Oscillators
- 2018
-
Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 9:1
-
Tidskriftsartikel (refereegranskat)abstract
- We use micromagnetic simulations to map out and compare the linear and auto-oscillating modes in constriction-based spin Hall nano-oscillators as a function of the applied magnetic field with a varying magnitude and out-of-plane angle. We demonstrate that, for all possible applied field configurations, the auto-oscillations emerge from the localized linear modes of the constriction. For field directions tending towards the plane, these modes are of the so-called edge type, i.e., localized at the opposite edges of the constriction. By contrast, when the magnetization direction approaches the film normal, the modes transform to the so-called bulk type, i.e., localized inside the constriction with substantially increased precession volume, consistent with the redistribution of the magnetic charges from the edges to the top and bottom surfaces of the constriction. In general, the threshold current of the corresponding auto-oscillations increases with the applied field strength and decreases with its out-of-plane angle, consistent with the behavior of the internal field and in good agreement with a macrospin model. A quantitative agreement is then achieved by taking into account the strongly nonuniform character of the system via a mean-field approximation. Both the Oersted (Oe) field and the spin-transfer torque from the drive current increase the localization and decrease the frequency of the observed mode. Furthermore, the antisymmetric Oe field breaks the lateral symmetry, favoring the localized mode at one of the two constriction edges, particularly for large out-of-plane field angles where the threshold current is significantly increased and the edge demagnetization is suppressed.
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| 25. |
- Feliciano, Gustavo T., et al.
(författare)
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Capacitive DNA Detection Driven by Electronic Charge Fluctuations in a Graphene Nanopore
- 2015
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Ingår i: Physical Review Applied. - 2331-7019. ; 3:3
-
Tidskriftsartikel (refereegranskat)abstract
- The advent of parallelized automated methods for rapid whole-genome analysis has led to an exponential drop in costs, thus greatly accelerating biomedical research and discovery. Third-generation sequencing techniques, which would utilize the characteristic electrical conductance of the four different nucleotides, could facilitate longer base read lengths and an even lower price per genome. In this work, we propose and apply a quantum-classical hybrid methodology to quantitatively determine the influence of the solvent on the dynamics of DNA and the resulting electron transport properties of a prototypic sequencing device utilizing a graphene nanopore through which the nucleic-acid chain is threaded. Our results show that charge fluctuations in the nucleotides are responsible for characteristic conductance modulations in this system, which can be regarded as a field-effect transistor tuned by the dynamic aqueous environment.
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| 26. |
- Fuertes Marrón, D., et al.
(författare)
-
Quantitative Determination of Luminescent Coupling in Multijunction Solar Cells from Spectral Photovoltage Measurements
- 2016
-
Ingår i: Physical Review Applied. - 2331-7019. ; 6:1
-
Tidskriftsartikel (refereegranskat)abstract
- We present a simple method to quantify the magnitude of luminescent coupling (LC) between stacked subcells in multijunction photovoltaic devices. The effect of luminescence produced at high-band-gap subcells on underlying low-gap units within the same device can be directly accessed as a measurable open-circuit voltage difference by comparing two photovoltage spectra. Additionally, our study unambiguously identifies LC as the modulation mechanism across multijunction solar cells generating a response from buried subcells in photoreflectance measurements.
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| 27. |
- Galin, M. A., et al.
(författare)
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Direct Visualization of Phase-Locking of Large Josephson Junction Arrays by Surface Electromagnetic Waves
- 2020
-
Ingår i: Physical Review Applied. - 2331-7019. ; 14:2
-
Tidskriftsartikel (refereegranskat)abstract
- Phase-locking of oscillators leads to super-radiant amplification of the emission power. This is particularly important for development of terahertz sources, which suffer from low emission efficiency. In this work we study large Josephson junction arrays containing several thousand Nb-based junctions. Using low-temperature scanning laser microscopy, we observe that at certain bias conditions two-dimensional standing-wave patterns are formed, manifesting themselves as global synchronization of the arrays. Analysis of standing waves indicates that they are formed by surface plasmon-type electromagnetic waves propagating at the electrode-substrate interface. Thus, we demonstrate that surface waves provide an effective mechanism for long-range coupling and phase-locking of large junction arrays.
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| 28. |
- Galin, Mikhail A., et al.
(författare)
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Synchronization of Large Josephson-Junction Arrays by Traveling Electromagnetic Waves
- 2018
-
Ingår i: Physical Review Applied. - 2331-7019. ; 9:5
-
Tidskriftsartikel (refereegranskat)abstract
- Mutual synchronization of many Josephson junctions is required for superradiant enhancement of the emission power. However, the larger the junction array is, the more difficult is the synchronization, especially when the array size becomes much larger than the emitted wavelength. Here, we study experimentally Josephson emission from such larger-than-the-wavelength Nb/NbSi/Nb junction arrays. For one of the arrays we observe a clear superradiant enhancement of emission above a threshold number of active junctions. The arrays exhibit strong geometrical resonances, seen as steps in current-voltage characteristics. However, radiation patterns of the arrays have forward-backward asymmetry, which is inconsistent with the solely geometrical resonance (standing-wave) mechanism of synchronization. We argue that the asymmetry provides evidence for an alternative mechanism of synchronization mediated by unidirectional traveling-wave propagation along the array (such as a surface plasmon). In this case, emission occurs predominantly in the direction of propagation of the traveling wave. Our conclusions are supported by numerical modeling of Josephson traveling-wave antenna. We argue that such a nonresonant mechanism of synchronization opens a possibility for phase locking of very large arrays of oscillators.
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| 29. |
- Gandhi, Hemi H., et al.
(författare)
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Gold-Hyperdoped Germanium with Room-Temperature Sub-Band-Gap Optoelectronic Response
- 2020
-
Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 14:6
-
Tidskriftsartikel (refereegranskat)abstract
- Short-wavelength-infrared (SWIR; 1.4-3.0 mu m) photodetection is important for various applications. Inducing a low-cost silicon-compatible material, such as germanium, to detect SWIR light would be advantageous for SWIR applications compared with using conventional (III-V or II-VI) SWIR materials. Here, we present a scalable nonequilibrium method for hyperdoping germanium with gold for dopant-mediated SWIR photodetection. Using ion implantation followed by nanosecond pulsed laser melting, we obtain a single-crystal material with a peak gold concentration of 3 x 10(19) cm(-3) (10(3) times the solubility limit). This hyperdoped germanium has fundamentally different optoelectronic properties from those of intrinsic and conventionally doped germanium. This material exhibits sub-band-gap absorption of light up to wavelengths of at least 3 mu m, with a sub-band-gap optical absorption coefficient comparable to that of commercial SWIR photodetection materials. We show that germanium hyperdoped with gold exhibits sub-band-gap SWIR photodetection at room temperature, in contrast with previous doped-germanium photodetector studies, which only show a low-temperature response. This material is a potential pathway to low-cost room-temperature silicon-compatible SWIR photodetection.
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| 30. |
- Garofalo, Fabio, et al.
(författare)
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Performance Study of Acoustophoretic Microfluidic Silicon-Glass Devices by Characterization of Material- and Geometry-Dependent Frequency Spectra
- 2017
-
Ingår i: Physical Review Applied. - 2331-7019. ; 7:5
-
Tidskriftsartikel (refereegranskat)abstract
- The mechanical and electrical response of acoustophoretic microfluidic devices attached to an ac-voltage-driven piezoelectric transducer is studied by means of numerical simulations. The governing equations are formulated in a variational framework that, introducing Lagrangian and Hamiltonian densities, is used to derive the weak form for the finite-element discretization of the equations and to characterize the device response in terms of frequency-dependent figures of merit or indicators. The effectiveness of the device in focusing microparticles is quantified by two mechanical indicators: the average direction of the pressure gradient and the amount of acoustic energy localized in the microchannel. Furthermore, we derive the relations between the Lagrangian, the Hamiltonian, and three electrical indicators: the resonance Q value, the impedance, and the electric power. The frequency response of the hard-to-measure mechanical indicators is correlated to that of the easy-to-measure electrical indicators, and, by introducing optimality criteria, it is clarified to which extent the latter suffices to identify optimal driving frequencies as the geometric configuration and the material parameters vary. The latter have been varied by considering both Pyrex and aluminium nitroxide top-lid materials.
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| 31. |
- Gasparinetti, S., et al.
(författare)
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Fast Electron Thermometry for Ultrasensitive Calorimetric Detection
- 2015
-
Ingår i: Physical Review Applied. - 2331-7019. ; 3:1
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate radio-frequency thermometry on a micrometer-sized metallic island below 100 mK. Our device is based on a normal-metal-insulator-superconductor tunnel junction coupled to a resonator with transmission readout. In the first generation of the device, we achieve 90 mu K/root Hz noise-equivalent temperature with 10 MHz bandwidth. We measure the thermal relaxation time of the electron gas in the island, which we find to be of the order of 100 mu s. Such a calorimetric detector, upon optimization, can be seamlessly integrated into superconducting circuits, with immediate applications in quantum-thermodynamics experiments down to single quanta of energy.
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| 32. |
- Golod, Taras, et al.
(författare)
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Planar Superconductor-Ferromagnet-Superconductor Josephson Junctions as Scanning-Probe Sensors
- 2019
-
Ingår i: Physical Review Applied. - 2331-7019. ; 11:1
-
Tidskriftsartikel (refereegranskat)abstract
- We propose a magnetic scanning-probe sensor based on a single-planar Josephson junction with a magnetic barrier. The planar geometry together with the high magnetic permeability of the barrier facilitates a double flux-focusing effect, which helps to guide magnetic flux into the junction and thus enhances field sensitivity of the sensor. We fabricate and analyze experimentally sensor prototypes with a superparamagnetic Cu−Ni and a ferromagnetic Ni barrier. We demonstrate that the planar geometry allows easy miniaturization to nanometer scale and facilitates an effective utilization of the self-field phenomenon for amplification of sensitivity and a simple implementation of a control line for feedback operation over a broad dynamic range. We argue that the proposed sensor can outperform equally sized superconducting quantum-interference devices (SQUIDs) both in terms of magnetic-field sensitivity and spatial resolution, which makes it advantageous for scanning-probe microscopy.
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| 33. |
- Golubev, Dmitry, et al.
(författare)
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Single-Photon Detection with a Josephson Junction Coupled to a Resonator
- 2021
-
Ingår i: Physical Review Applied. - 2331-7019. ; 16:1
-
Tidskriftsartikel (refereegranskat)abstract
- We use a semiclassical formalism to optimize a microwave single-photon detector based on switching events of a current-biased Josephson junction coupled to a resonator. To detect very rare events, the average time between dark counts τdark should be maximized taking into account that the switching time τsw should be sufficiently small. We demonstrate that these times can be tuned in a wide range by changing the junction parameters, and τdark/τsw∼109 can be achieved. Therefore, a junction-resonator arrangement can be used to detect extremely low photon fluxes (e.g., for searching for galactic axions).
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| 34. |
- Grebenchuk, S. Yu, et al.
(författare)
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Nonlocal Long-Range Synchronization of Planar Josephson-Junction Arrays
- 2022
-
Ingår i: Physical Review Applied. - 2331-7019. ; 17:6
-
Tidskriftsartikel (refereegranskat)abstract
- We study arrays of planar Nb Josephson junctions with contacts to intermediate electrodes, which allow measurements of individual junctions and, thus, provide an insight into intricate array dynamics. We observe strong indications for array phase locking, despite a significant interjunction separation. Several unusual phenomena are reported, such as a bistable critical current with reentrant superconductivity upon switching of nearby junctions; and “incorrect” Shapiro steps, occurring at mixing frequencies between the external rf radiation and the internal Josephson frequency in nearby junctions. Our results reveal a surprisingly strong and long-range interjunction interaction, which is attributed to nonlocality of planar-junction electrodynamics, caused by the long-range spreading of stray electromagnetic fields. The nonlocality greatly enhances the high-frequency interjunction coupling and enables large-scale synchronization. Therefore, we conclude that planar geometry is advantageous for the realization of coherent Josephson electronics.
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| 35. |
- Gregefalk, Anton, et al.
(författare)
-
Transitionless quantum driving in spin echo
- 2022
-
Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 17
-
Tidskriftsartikel (refereegranskat)abstract
- Spin echo can be used to refocus random dynamical phases caused by inhomogeneities in control fields and thereby retain the purity of a spatial distribution of quantum spins. This technique for accurate spin control is an essential ingredient in many applications, such as nuclear magnetic resonance, magnetic resonance imaging, and quantum information processing. Here, we show how all the elements of a spin echo sequence can be performed at high speed by means of transitionless quantum driving. This technique promises accurate control of rapid quantum spin evolution. We apply the scheme to universal nonadiabatic geometric single- and two-qubit gates in a nuclear magnetic resonance setting.
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| 36. |
- Guénot, Diego, et al.
(författare)
-
Distribution of Liquid Mass in Transient Sprays Measured Using Laser-Plasma-Driven X-Ray Tomography
- 2022
-
Ingår i: Physical Review Applied. - 2331-7019. ; 17:6
-
Tidskriftsartikel (refereegranskat)abstract
- We report, the use of laser-plasma-driven x rays to reveal the three-dimensional (3D) structure of a highly atomizing water spray. Soft x rays approximately 5 keV are generated by means of a laser-plasma accelerator. Transmission radiography measurements are performed at different angles, by rotating a multihole injector. Using computer tomography, the local liquid volume distribution and its spatial variation are retrieved in 3D, showing up to 55% liquid fraction at the nozzle outlet, which decreases to below 7% within only 1 mm. The resolution of the liquid volume fraction is 0.5% while the spatial resolution of the radiographic images is 11.5μm. The x-ray source used here provides successful measurements of liquid mass distribution over a relatively large volume and is very promising for the analysis of a variety of challenging transient spray systems, e.g., the injection of liquid synthetic and biofuels used for future clean-combustion applications.
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| 37. |
- Gutierrez Latorre, Martí, 1993, et al.
(författare)
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Superconducting Microsphere Magnetically Levitated in an Anharmonic Potential with Integrated Magnetic Readout
- 2023
-
Ingår i: Physical Review Applied. - 2331-7019. ; 19:5
-
Tidskriftsartikel (refereegranskat)abstract
- Magnetically levitated superconducting microparticles offer a promising path to quantum experiments with picogram to microgram objects. In this work, we levitate a 700 ng∼1017amu superconducting microsphere in a magnetic chip trap in which detection is integrated. We measure the center-of-mass motion of the particle using a dc superconducting quantum interference device magnetometer. The trap frequencies are continuously tunable between 30 and 160 Hz and the particle remains stably trapped over days in a dilution-refrigerator environment. We characterize the motional-amplitude-dependent frequency shifts, which arise from trap anharmonicities, namely, Duffing nonlinearities and mode couplings. We explain this nonlinear behavior using finite-element modeling of the chip-based trap potential. This work may constitute a first step toward quantum experiments and ultrasensitive inertial sensors with magnetically levitated superconducting microparticles.
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| 38. |
- Havers, Megan, et al.
(författare)
-
Silica seed particles improve the efficiency and throughput of nanoparticle acoustic trapping
- 2024
-
Ingår i: Physical Review Applied. - 2331-7019. ; 21:3
-
Tidskriftsartikel (refereegranskat)abstract
- Silica has rarely been used as a seed particle material in acoustic trapping of nanoparticles. Here we use fluorescent nanoparticles, which are frequently used as a model system, to demonstrate that throughput and nanoparticle trapping efficiency can be improved by using silica seed particles as opposed to traditionally used polystyrene seed particles. The 10 times larger dipole scattering coefficient of silica seed particles compared with polystyrene seed particles in water leads to a higher retention force against fluid flow and thus enables higher throughput. Seed particles retained at an actuation voltage of approximately 10 V p.p. can withstand flow rates up to 2100 ± 200 μl/min for silica and 200 ± 50 μl/min for polystyrene. Furthermore, silica is found to be 40%-2000% more efficient (number of trapped nanoparticles as measured by fluorescent intensity) than polystyrene seed particles in trapping 270-nm polystyrene nanoparticles from suspensions of 1010-1011 particles/ml. Moreover, after enriching nanoparticles into a silica seed particle cluster, the washing flow rate can be increased from 30 μl/min to 200 μl/min (the flow rate at which polystyrene clusters are unstable), halving the total sample processing time without losing the silica seed particle cluster or compromising the nanoparticle trapping efficiency. Thus, material properties (particularly density) of the seed particles are critical to both nanoparticle trapping efficiency and throughput.
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| 39. |
- Hemachandran, E., et al.
(författare)
-
Continuous Droplet Coalescence in a Microchannel Coflow Using Bulk Acoustic Waves
- 2019
-
Ingår i: Physical Review Applied. - 2331-7019. ; 12:4
-
Tidskriftsartikel (refereegranskat)abstract
- The coalescence of liquid droplets with a liquid stream has profound importance in various emerging applications, such as biochemical assays. Acoustic force-based droplet manipulation, which offers unique advantages, is consequently gaining attention. However, the physics of acoustics-driven coalescence of liquid droplets with a liquid stream is not well understood. Here, we unravel the mechanism of coalescence of aqueous droplets flowing in an immiscible (oil) phase with a coflowing aqueous stream, when the system is exposed to acoustic radiation force due to bulk acoustic waves. Our study reveals that the acoustic coalescence phenomenon is governed by the interplay between two important timescales, acoustic migration timescale (τac) and advection timescale (τadv), that underpin the phenomenon. We find that the phenomenon is also governed by the acoustic capillary number (Cac) and relative widths of the coflowing oil and aqueous streams (i.e., Waq and Woil). Our results show that, if Cac<0.9 and Waq>Woil are satisfied to ensure the stability of the streams and positioning of the acoustic node in the aqueous phase, respectively, continuous coalescence is observed for (τadv/τac)≥0.85. We exploit the phenomenon for the extraction of droplet contents (beads and cells) into an aqueous stream.
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| 40. |
- Hillmann, Timo, 1995, et al.
(författare)
-
Designing Kerr Interactions for Quantum Information Processing via Counterrotating Terms of Asymmetric Josephson-Junction Loops
- 2022
-
Ingår i: Physical Review Applied. - 2331-7019. ; 17:6
-
Tidskriftsartikel (refereegranskat)abstract
- Continuous-variable systems realized in high-coherence microwave cavities are a promising platform for quantum information processing. While strong dynamic nonlinear interactions are desired to implement fast and high-fidelity quantum operations, static cavity nonlinearities typically limit the performance of bosonic quantum error-correcting codes. Here we study theoretical models of nonlinear oscillators describing superconducting quantum circuits with asymmetric Josephson-junction loops. Treating the nonlinearity as a perturbation, we derive effective Hamiltonians using the Schrieffer-Wolff transformation. We support our analytical results by numerical experiments and show that the effective Kerr-type couplings can be canceled by an interplay of higher-order nonlinearities. This can be better understood in a simplified model supporting only cubic and quartic nonlinearities. Our results show that a cubic interaction allows an increase in the effective rates of both linear and nonlinear operations without an increase in the undesired anharmonicity of an oscillator which is crucial for many bosonic encodings.
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| 41. |
- Holeňák, Radek, et al.
(författare)
-
Assessing trajectory-dependent electronic energy loss of keV ions by a binary collision approximation code
- 2024
-
Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 21:2
-
Tidskriftsartikel (refereegranskat)abstract
- The inelastic energy deposition of energetic ions is a decisive quantity for numerous industrial-scale applications, such as sputtering and ion implantation, yet the underlying physics being governed by dynamic many-particle processes is commonly only qualitatively understood. Recently, transmission experiments on single-crystalline targets (Phys. Rev. Lett. 124, 096601 & Phys. Rev. A 102, 062803) revealed a complex energy scaling of the inelastic energy loss of low-energy ions heavier than protons along different trajectories. We use a Monte Carlo like binary collision approximation code equipped with an impact-parameter-dependent modeling of the inelastic energy losses to assess the role of local contributions to electronic excitations in these cases. We compare angular intensity distributions of calculated trajectories with experimental results for 50-keV 4He and 100-keV 29Si ions transmitted in a time-of-flight setup through single-crystalline silicon (001) foils with nominal thicknesses of 200 and 50 nm, respectively. In these calculations, we employ different models of electronic energy loss, i.e., local and nonlocal forms for light and heavy projectiles. We find that the vast number of projectiles are eventually channeled along their trajectories, regardless of the alignment of the crystal with respect to the incident beam. It is, however, only when local electronic energy loss is considered that the simulated two-dimensional maps and energy distributions show excellent agreement with the experimental results, where channeling leads to significantly reduced stopping, especially for heavier projectiles. We demonstrate the relevance of these effects for ion implantations by assessing the nonlinear and nonmonotonic scaling of the ion range with the thickness of a random surface layer.
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| 42. |
- Holm, Stefan H., et al.
(författare)
-
Microfluidic Particle Sorting in Concentrated Erythrocyte Suspensions
- 2019
-
Ingår i: Physical Review Applied. - 2331-7019. ; 12:1
-
Tidskriftsartikel (refereegranskat)abstract
- An important step in diagnostics is the isolation of specific cells and microorganisms of interest from blood. Since such bioparticles are often present at very low concentrations, throughput needs to be as high as possible. In addition, to ensure simplicity, a minimum of sample preparation is important. Therefore, sorting schemes that function for whole blood are highly desirable. Deterministic lateral displacement (DLD) devices have proven to be very precise and versatile in terms of a wide range of sorting parameters. To better understand how DLD devices perform for blood as the hematocrit increases, we carry out measurements and simulations for spherical particles in the micrometer range which move through DLD arrays for different flow velocities and hematocrits ranging from pure buffer to concentrated erythrocyte suspensions mimicking whole blood. We find that the separation function of the DLD array is sustained even though the blood cells introduce a shift in the trajectories and a significant dispersion for particles whose diameters are close to the critical size in the device. Simulations qualitatively replicate our experimental observations and help us identify fundamental mechanisms for the effect of hematocrit on the performance of the DLD device.
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| 43. |
- Houshang, Afshin, et al.
(författare)
-
Phase-Binarized Spin Hall Nano-Oscillator Arrays: Towards Spin Hall Ising Machines
- 2022
-
Ingår i: Physical Review Applied. - 2331-7019. ; 17:1
-
Tidskriftsartikel (refereegranskat)abstract
- Ising machines (IMs) are physical systems designed to find solutions to combinatorial optimization (CO) problems mapped onto the IM via the coupling strengths between its binary spins. Using its intrinsic dynamics and different annealing schemes, the IM relaxes over time to its lowest-energy state, which is the solution to the CO problem. IMs have been implemented on different platforms, and interacting nonlinear oscillators are particularly promising candidates. Here we demonstrate a pathway towards an oscillator-based IM using arrays of nanoconstriction spin Hall nano-oscillators (SHNOs). We show how SHNOs can be readily phase binarized and how their resulting microwave power corresponds to well-defined global phase states. To distinguish between degenerate states, we use phase-resolved Brillouin-light-scattering microscopy and directly observe the individual phase of each nanoconstriction. Micromagnetic simulations corroborate our experiments and confirm that our proposed IM platform can solve CO problems, showcased by how the phase states of a 2 x 2 SHNO array are solutions to a modified max-cut problem. Compared with the commercially available D-Wave Advantage (TM), our architecture holds significant promise for faster sampling, substantially reduced power consumption, and a dramatically smaller footprint.
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| 44. |
- Hovhannisyan, Razmik A., et al.
(författare)
-
Superresolution magnetic imaging by a Josephson junction via holographic reconstruction of I c ( H ) modulation
- 2023
-
Ingår i: Physical Review Applied. - 2331-7019. ; 20:6
-
Tidskriftsartikel (refereegranskat)abstract
- This work provides a proof -of -concept for superresolution magnetic imaging using a single Josephson junction. The technique resembles digital holography: magnetic patterns are obtained via an inverseproblem solution from diffractionlike modulation of the junction's critical current, I c (H) . We demonstrate numerical reconstruction of complex two-dimensional patterns, verify the technique experimentally using Nb-based planar junctions, and fabricate an operational sensor on a cantilever. Our results show that Josephson holography allows for both high spatial resolution (approximately 20 nm) and high field sensitivity (approximately 10 - 11 T R root Hz), thus resolving the trade-off problem between resolution and sensitivity in magnetic scanning probe imaging.
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| 45. |
- Hu, Chang-Kang, et al.
(författare)
-
Native Conditional iSWAP Operation with Superconducting Artificial Atoms
- 2023
-
Ingår i: Physical Review Applied. - 2331-7019. ; 20:3
-
Tidskriftsartikel (refereegranskat)abstract
- Controlling the flow of quantum information is a fundamental task for quantum computers, which is unfeasible to realize on classical devices. Coherent devices, which can process quantum states are thus required to route the quantum states that encode information. In this paper we demonstrate experimentally the smallest quantum transistor with a superconducting quantum processor, which is composed of a collector qubit, an emitter qubit, and a coupler (transistor gate). The interaction strength between the collector and emitter qubits is controlled by the frequency and state of the coupler, effectively implementing a quantum switch. Through the coupler-state-dependent Heisenberg (inherent) interaction between the qubits, a single-step (native) conditional iSWAP operation can be applied. To this end, we find that it is useful to take into consideration the higher-energy level for achieving a native and high-fidelity transistor operation. By reconstructing the quantum process tomography, we obtain an operation fidelity of 92.36% when the transistor gate is open (iSWAP implementation) and 95.23% in the case of closed gate (identity gate implementation). The architecture has strong potential in quantum information processing applications with superconducting qubits.
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| 46. |
- Huang, Shuo, et al.
(författare)
-
Strengthening Induced by MagnetoChemical Transition in Al-Doped Fe-Cr-Co-Ni High-Entropy Alloys
- 2018
-
Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 10:6
-
Tidskriftsartikel (refereegranskat)abstract
- Alloys with adjustable mechanical performance are of fundamental interest in material designs. Here, we investigate the magnetic- and chemical-ordering behavior of the ferromagnetic Fe-Cr-Co-Ni-Al-x (1 <= x <= 2.5) high-entropy alloys with the help of first-principle alloy theory. The lattice constants and the single- and polycrystalline elastic parameters for partially ordered and random structures are considered. In contrast to the trend found for the completely disordered phase, we demonstrate that ordering driven primarily by Al results in an enhanced Young's modulus, especially at high-Al concentrations, which is in line with the observed increase of the hardness for systems with a body-centered-cubic underlying lattice. The results suggest that outstanding strength and ductility can be realized by proper control of the ordering level in single- and multiphase high-entropy alloys.
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| 47. |
- Huang, Yuqing, et al.
(författare)
-
Effect of a Phonon Bottleneck on Exciton and Spin Generation in Self-Assembled In1-xGaxAs Quantum Dots
- 2018
-
Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 9:4
-
Tidskriftsartikel (refereegranskat)abstract
- We provide direct experimental evidence for the effect of a phonon bottleneck on exciton and spin generation in self-assembled In0.5Ga0.5As quantum dots (QDs). With the aid of tunable laser spectroscopy, we resolve and identify efficient exciton generation channels in the QDs mediated by longitudinal-optical (LO) phonons from an otherwise inhomogeneously broadened QD emission background that suffers from the phonon bottleneck effect in exciton generation. Spin-generation efficiency is found to be enhanced under the LO-assisted excitation condition due to suppressed spin relaxation accompanying accelerated exciton generation. These findings underline the importance of fine-tuning QD energy levels that will benefit potential spin-optoelectronic applications of QDs by reducing spin loss due to the phonon bottleneck.
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| 48. |
- Huang, Yuqing, et al.
(författare)
-
Oblique Nuclear Quadrupole Interaction in Self-Assembled Structures Based on Semiconductor Quantum Dots
- 2020
-
Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 14:4
-
Tidskriftsartikel (refereegranskat)abstract
- Dynamic nuclear polarization (DNP) is well recognized as being important in spintronics and quantum-information processing. DNP gives rise to high nuclear spin polarization that not only can prolong electron-spin lifetime by generating an Overhauser field (OHF), but also has fertilized the idea to explore nuclear spin qubits. In strained quantum-dot structures (QDSs), a nuclear spin is coupled to a strain field via its quadrupole moment. It has been shown that such nuclear quadrupole interaction (NQI) can be used to achieve appreciable DNP and hence electron-spin polarization. Here, we uncover magneto-optical anomalies from a series of laterally arranged (In,Ga)As QDSs that arise from the NQI and DNP in these nanostructures. We find that the principal axis of NQI in symmetry-lowered QDSs significantly deviates from the growth direction, resulting in tilting of OHF with an angle exceeding 37 degrees. The resulting transverse component of OHF is probed with respect to the crystallographic orientations and its influence on the DNP and ensemble spin dephasing is analyzed. We show that a high-symmetry electronic confinement potential for excitons does not guarantee a high-symmetry NQI for nuclei within the same nano-object, thereby calling for correlated optimization in the symmetry of the electronic confinement potential and that of the nuclear spin bath. Our results underline the role of oblique NQI in electron-spin decoherence and depolarization, which has so far largely been overlooked. This work thus sheds light on design rules for engineering the electronic and spin landscape of QDSs for better performance of DNP desirable for applications in spintronics and quantum computation.
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| 49. |
- Huang, Yuqing, et al.
(författare)
-
Tuneable Nonlinear Spin Response in a Nonmagnetic Semiconductor
- 2023
-
Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 19:6
-
Tidskriftsartikel (refereegranskat)abstract
- Nonlinear effects and dynamics are found in a wide range of research fields. In magnetic materials, nonlinear spin dynamics enables ultrafast manipulation of spin, which promises high-speed nonvolatile information processing and storage for future spintronic applications. However, a nonlinear spin response is not yet demonstrated in a nonmagnetic material that lacks strong magnetic interactions. Dilute nitride III-V materials, e.g., (Ga, N)As, have the ability to amplify the conduction-electron-spin polarization by filtering out minority spins via spin-polarized defect states at room temperature. Here, by employing coupled rate equations, we theoretically demonstrate the emergence of a nonlinear spin response in such a defect-enabled room-temperature spin amplifier. Furthermore, we showcase the proposed spin nonlinearity in a (Ga, N)As-InAs quantum dot (QD) coupled all-semiconductor nanostructure, by measuring the higher-harmonic generation, which converts the modulation of excitation polarization into the second-, third-, and fourth-order harmonic oscillations of the QDs photoluminescence intensity and polarization. The observed spin nonlinearity originates from defect-mediated spin-dependent recombination, which can be conveniently tuned with an external magnetic field and can potentially operate at a speed exceeding 1 GHz. The demonstrated spin nonlinearity could pave the way for nonlinear spintronic and optospintronic device applications based on nonmagnetic semiconductors with simultaneously achievable high operation speed and nonlinear response.
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| 50. |
- Iacocca, Ezio, 1986, et al.
(författare)
-
Topologically Nontrivial Magnon Bands in Artificial Square Spin Ices with Dzyaloshinskii-Moriya Interaction
- 2017
-
Ingår i: Physical Review Applied. - 2331-7019. ; 8:3, s. 034015-
-
Tidskriftsartikel (refereegranskat)abstract
- Systems that exhibit topologically protected edge states are interesting both from a fundamental point of view as well as for potential applications, the latter because of the absence of backscattering and robustness to perturbations. It is desirable to be able to control and manipulate such edge states. Here, we show that artificial square ices can incorporate both features: an interfacial Dzyaloshinskii-Moriya interaction gives rise to topologically nontrivial magnon bands, and the equilibrium state of the spin ice is reconfigurable with different configurations having different magnon dispersions and topology. The topology is found to develop as odd-symmetry bulk and edge magnon bands approach each other so that constructive band inversion occurs in reciprocal space. Our results show that topologically protected bands are supported in square spin ices.
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