1. 
 Alarcon, Alvaro, et al.
(författare)

FewModeFiber Technology Finetunes Losses in Quantum Communication Systems
 2021

Ingår i: Physical Review Applied.  : AMER PHYSICAL SOC.  23317019. ; 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 singlephoton time bins has become widely adopted. It, however, introduces a fundamental loss, which increases with the dimension and limits its application over long distances. Here solve this longstanding hurdle by using a fewmodefiber spacedivisionmultiplexing platform working with orbitalangularmomentum modes. In our scheme, we maintain the practicability provided by the timebin scheme, while the quantum states are transmitted through a fewmode fiber in a configuration that does not introduce postselection losses. We experimentally demonstrate our proposal by successfully transmitting phaseencoded singlephoton states for quantum cryptography over 500 m of fewmode fiber, showing the feasibility of our scheme.


2. 
 Anghel, D. V., et al.
(författare)

ColdElectron Bolometer as a 1cmWavelength Photon Counter
 2020

Ingår i: Physical Review Applied.  23317019. ; 13:2

Tidskriftsartikel (refereegranskat)abstract
 We investigate theoretically the possibility of using the coldelectron bolometer (CEB) as a counter for 1cmwavelength (30GHz) 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 currentbiased regime is favorable due to lower noise and allows for photon counting at least below 50 mK. For the experimental setups investigated here, the voltagebiased CEBs may also work as photon counters but with less accuracy and, eventually, may require smaller volumes of the normalmetal island.


3. 
 Arora, Monika, et al.
(författare)

Magnetic Damping in Polycrystalline ThinFilm FeV Alloys
 2021

Ingår i: Physical Review Applied.  : American Physical Society.  23317019. ; 15:5

Tidskriftsartikel (refereegranskat)abstract
 We report on the magnetic damping properties of polycrystalline FeV 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 103, which is approximately a factor of 3 higher than our calculated value of 0.48 x 103. From firstprinciples 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.


4. 
 Aurino, Pier Paolo, 1985, et al.
(författare)

Retention of Electronic Conductivity in LaAlO3/SrTiO3 Nanostructures Using a SrCuO2 Capping Layer
 2016

Ingår i: Physical Review Applied.  : American Physical Society.  23317019. ; 6:2

Tidskriftsartikel (refereegranskat)abstract
 The interface between two wide bandgap 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 electricaltransport 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 quasi2DEG 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 roomtemperature electrical resistivity significantly increases when the structure size becomes smaller than 1 mu m. Highresolution 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.


5. 
 Baghdadi, Reza, 1984, et al.
(författare)

Fabricating Nanogaps in YBa2Cu3O7delta for Hybrid ProximityBased Josephson Junctions
 2015

Ingår i: Physical Review Applied.  23317019. ; 4:1

Tidskriftsartikel (refereegranskat)abstract
 The advances of nanotechnologies applied to highcriticaltemperature 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 asgrown bulk material at the nanoscale. Here we present a fabrication approach allowing the realization of YBa2Cu3O7delta (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 currentvoltage 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 vortexentry 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 magneticfield 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.


6. 
 Bejanin, J. H., et al.
(författare)

ThreeDimensional Wiring for Extensible Quantum Computing: The Quantum Socket
 2016

Ingår i: Physical Review Applied.  23317019. ; 6:4

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 errorcorrection 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 solidstate 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 twodimensional methods based on wire bonding. The quantum socket is based on springmounted microwiresthe threedimensional wiresthat 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 solidstate 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 highquality superconducting resonators at a temperature of approximately 10 mK. Quantum errorcorrection codes such as the surface code will largely benefit from the quantum socket, which will make it possible to address qubits located on a twodimensional 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.


7. 
 Bengtsson, Andreas, 1991, et al.
(författare)

Improved Success Probability with Greater Circuit Depth for the Quantum Approximate Optimization Algorithm
 2020

Ingår i: Physical Review Applied.  23317019. ; 14:3

Tidskriftsartikel (refereegranskat)abstract
 Presentday, noisy, small or intermediatescale quantum processorsalthough far from fault tolerantsupport the execution of heuristic quantum algorithms, which might enable a quantum advantage, for example, when applied to combinatorial optimization problems. On smallscale 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 exactcover problem, with 96.6% success probability, by iterating the algorithm up to level two.


8. 
 Booker, Ian Don, et al.
(författare)

Oxidationinduced deep levels in n and ptype 4H and 6HSiC and their influence on carrier lifetime
 2016

Ingår i: Physical Review Applied.  : American Physical Society.  23317019. ; 6:1, s. 115

Tidskriftsartikel (refereegranskat)abstract
 We present a complete analysis of the electron and holecapture and emission processes of the deep levels ON1, ON2a, and ON2b in 4HSiC and their 6HSiC 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 highresolution capacitance deeplevel transient spectroscopy spectra measured with different fillingpulse lengths in n and ptype material. All defects are found to be doubledonortype positiveU twolevel defects with very small holecapture cross sections, making them recombination centers of low efficiency, in accordance with minoritycarrierlifetime 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.


9. 
 Borgani, Riccardo, et al.
(författare)

BackgroundForce Compensation in Dynamic Atomic Force Microscopy
 2017

Ingår i: Physical Review Applied.  : AMER PHYSICAL SOC.  23317019. ; 7:6

Tidskriftsartikel (refereegranskat)abstract
 Background forces are linear longrange interactions of the cantilever body with its surroundings that must be compensated for in order to reveal tipsurface 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 linearresponse 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.


10. 
 Borgani, Riccardo, et al.
(författare)

Fast Multifrequency Measurement of Nonlinear Conductance
 2019

Ingår i: Physical Review Applied.  : American Physical Society.  23317019. ; 11:4

Tidskriftsartikel (refereegranskat)abstract
 We describe a phasecoherent multifrequency lockin measurement technique that uses the inverse Fourier transform to reconstruct the nonlinear currentvoltage 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 currentvoltage characteristics at every pixel while scanning at standard imaging speed.

