| 1. |
- Shiri, Daryoush, 1975, et al.
(författare)
-
An Electrically Controlled Heat Rectifier using Graphene Nanoribbons
- 2019
-
Ingår i: 2019 IEEE 14th Nanotechnology Materials and Devices Conference, NMDC 2019. - 2378-377X. - 9781728126371 ; October 2019, s. 1-4
-
Konferensbidrag (refereegranskat)abstract
- Using Molecular Dynamics (MD) simulations we propose that splitting a graphene nanoribbon into two unequal strained sections using external force leads to large asymmetry in the forward and reverse heat fluxes. We find that the corresponding rectification ratio (RR) is enhanced to 60% compared to previous proposals. More importantly, the polarity of the proposed heat diode is controllable on-the-fly i.e. by changing the position where force is applied. This technique obviates the complex nano-patterning and lithography required to pattern graphene every time a new rectification value or sign is sought for and opens a route to simpler fabrication of phononic devices in 2D materials.
|
|
| 2. |
- Shiri, Daryoush, 1975, et al.
(författare)
-
Gunn-Hilsum Effect in Mechanically Strained Silicon Nanowires: Tunable Negative Differential Resistance
- 2018
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 8:1
-
Tidskriftsartikel (refereegranskat)abstract
- Gunn (or Gunn-Hilsum) Effect and its associated negative differential resistivity (NDR) emanates from transfer of electrons between two different energy subbands. This effect was observed in semiconductors like GaAs which has a direct bandgap of very low effective mass and an indirect subband of high effective mass which lies ~300 meV above the former. In contrast to GaAs, bulk silicon has a very high energy spacing (~1 eV) which renders the initiation of transfer-induced NDR unobservable. Using Density Functional Theory (DFT), semi-empirical 10 orbital (sp 3 d 5 s ∗ ) Tight Binding and Ensemble Monte Carlo (EMC) methods we show for the first time that (a) Gunn Effect can be induced in silicon nanowires (SiNW) with diameters of 3.1 nm under +3% strain and an electric field of 5000 V/cm, (b) the onset of NDR in the I-V characteristics is reversibly adjustable by strain and (c) strain modulates the resistivity by a factor 2.3 for SiNWs of normal I-V characteristics i.e. those without NDR. These observations are promising for applications of SiNWs in electromechanical sensors and adjustable microwave oscillators. It is noteworthy that the observed NDC is different in principle from Esaki-Diode and Resonant Tunneling Diodes (RTD) in which NDR originates from tunneling effect.
|
|
| 3. |
- Shiri, Daryoush, 1975, et al.
(författare)
-
Heat-to-mechanical energy conversion in graphene: Manifestation of Umklapp enhancement with strain
- 2019
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 125:12
-
Tidskriftsartikel (refereegranskat)abstract
- Conversion of heat-flux from a steady state temperature difference to mechanical vibration is demonstrated in graphene nanoribbons using direct non-equilibrium molecular dynamics. We observe that this effect is independent of the method of imposing the temperature gradient, heat flux, as well as imposed boundary conditions. We propose that simply dividing the nanoribbon in long and short sections using a partially immobilized area will lead to excitation of long-wavelength vibrations into the long section of the nanoribbon. This results in simpler architectures for heat-to-vibration converter devices based on graphene. Furthermore, we observe that applying tensile axial strain to nanoribbons facilitates vibrational instability by reducing the required threshold heat flux or the temperature gradient. Finally, we discuss the role played by Umklapp scattering for physical mechanisms behind these observations.
|
|
| 4. |
- Anantram, M. P., et al.
(författare)
-
Quantum Mechanics for Engineers and Material Scientists: An Introduction
- 2024
-
Bok (övrigt vetenskapligt/konstnärligt)abstract
- This introductory book is aimed at students of engineering and material science who want to learn the necessary toolboxes of practical quantum mechanics. The authors have made sure that all the calculations are complete, and they have avoided the usage of the familiar phrase, “it can be easily shown” while being mathematically rigorous. Knowledge of the sophomore level introduction to ordinary differential equations is all that is needed. Well-designed and modern examples help the reader grasp and digest the concept before moving to the next one. The book offers a lucid exposition to the modern field of quantum computing and quantum gates, two-level systems, orbitals, spin, periodic solids, tunneling, and Fermi golden rule. The basics of electronic and optical properties of nanomaterials using the basics of quantum mechanics are presented without the reader getting lost in research articles with different notations and units. There are numerous examples in the book covering topics such as carbon nanotubes, graphene, superconducting qubits, principle of scanning tunneling microscopy, heterostructure based terahertz generation and negative differential resistance device, quantized LC circuit, Grover’s search algorithm, phase kickback, quantum dots, well, nanowires, quantum of conductance, ballistic conductor, spin-orbit coupling, and spin transistor. Authors use analogies based on familiar engineering concepts wherever possible to broaden the view of the reader. The philosophy behind the book is teaching by showing how it is done and using “pictures” which is worth 1000 words.
|
|
| 5. |
- Bejanin, J. H., et al.
(författare)
-
Three-Dimensional Wiring for Extensible Quantum Computing: The Quantum Socket
- 2016
-
Ingår i: Physical Review Applied. - 2331-7019. ; 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 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.
|
|
| 6. |
- 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. - 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.
|
|
| 7. |
- Fadavi Roudsari, Anita, 1978, et al.
(författare)
-
Three-wave mixing traveling-wave parametric amplifier with periodic variation of the circuit parameters
- 2023
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 122:5
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the implementation of a near-quantum-limited, traveling-wave parametric amplifier that uses three-wave mixing (3WM). To favor amplification by 3WM, we use superconducting nonlinear asymmetric inductive element (SNAIL) loops, biased with a dc magnetic flux. In addition, we equip the device with dispersion engineering features to create a stopband at the second harmonic of the pump and suppress the propagation of the higher harmonics that otherwise degrade the amplification. With a chain of 440 SNAILs, the amplifier provides up to 20 dB gain and a 3-dB bandwidth of 1 GHz. The added noise by the amplifier is found to be less than one photon.
|
|
| 8. |
- Grigoras, K., et al.
(författare)
-
Qubit-Compatible Substrates With Superconducting Through-Silicon Vias
- 2022
-
Ingår i: IEEE Transactions on Quantum Engineering. - 2689-1808. ; 3
-
Tidskriftsartikel (refereegranskat)abstract
- We fabricate and characterize superconducting through-silicon vias and electrodes suitable for superconducting quantum processors. We measure internal quality factors of a million for test resonators excited at single-photon levels, on chips with superconducting vias used to stitch ground planes on the front and back sides of the chips. This resonator performance is on par with the state of the art for silicon-based planar solutions, despite the presence of vias. Via stitching of ground planes is an important enabling technology for increasing the physical size of quantum processor chips, and is a first step toward more complex quantum devices with three-dimensional integration.
|
|
| 9. |
- Islam, Shadli, et al.
(författare)
-
Ab-initio Calculation of Nonlinear Optical Susceptibilities in Germanium Quantum Dots
- 2019
-
Ingår i: 2018 IEEE 13TH NANOTECHNOLOGY MATERIALS AND DEVICES CONFERENCE (NMDC). - 2378-377X. - 9781538610169 ; , s. 113-116
-
Konferensbidrag (refereegranskat)abstract
- Using Time Independent Density Functional Theory (TIDFT) implemented in SIESTA (R) we calculated the 2nd order and 3rd order nonlinear optical susceptibilities of small Germanium Quantum Dots (GeQD). We observe that the symmetry breaking due to surface termination enhances chi((2)) up to 299.1 pm/V which promises a strong Second Harmonic Generation (SHG) in GeQDs. Diagonal components for chi((2)) tensor are 52.5, 11.2, 299.1 pm/V, for xxx, yyy and zzz, respectively. The 3rd order susceptibility, chi((3)), is within the range of (0.2-0.4) x 10(-18) m(2)/V-2 which is close to the reported experimental values of bulk Germanium. This study suggests possibilities of enhancing SHG in GeQDs through symmetry breaking via strain and surface termination/reconstruction as well as suitability of this fast and less-computationally intensive Density Functional Theory (DFT)-based method in predicting nonlinear optical susceptibilities of nano structures.
|
|
| 10. |
- Kosen, Sandoko, 1991, et al.
(författare)
-
Building blocks of a flip-chip integrated superconducting quantum processor
- 2022
-
Ingår i: Quantum Science and Technology. - : IOP Publishing. - 2058-9565. ; 7:3
-
Tidskriftsartikel (refereegranskat)abstract
- We have integrated single and coupled superconducting transmon qubits into flip-chip modules. Each module consists of two chips-one quantum chip and one control chip-that are bump-bonded together. We demonstrate time-averaged coherence times exceeding 90 mu s, single-qubit gate fidelities exceeding 99.9%, and two-qubit gate fidelities above 98.6%. We also present device design methods and discuss the sensitivity of device parameters to variation in interchip spacing. Notably, the additional flip-chip fabrication steps do not degrade the qubit performance compared to our baseline state-of-the-art in single-chip, planar circuits. This integration technique can be extended to the realisation of quantum processors accommodating hundreds of qubits in one module as it offers adequate input/output wiring access to all qubits and couplers.
|
|
| 11. |
- Li, Hangxi, 1994, et al.
(författare)
-
Experimentally Verified, Fast Analytic, and Numerical Design of Superconducting Resonators in Flip-Chip Architectures
- 2023
-
Ingår i: IEEE Transactions on Quantum Engineering. ; 4
-
Tidskriftsartikel (refereegranskat)abstract
- In superconducting quantum processors, the predictability of device parameters is of increasing importance as many laboratories scale up their systems to larger sizes in a 3-D-integrated architecture. In particular, the properties of superconducting resonators must be controlled well to ensure high-fidelity multiplexed readout of qubits. Here, we present a method, based on conformal mapping techniques, to predict a resonator's parameters directly from its 2-D cross-section, without computationally heavy and time-consuming 3-D simulation. We demonstrate the method's validity by comparing the calculated resonator frequency and coupling quality factor with those obtained through 3-D finite-element-method simulation and by measurement of 15 resonators in a flip-chip-integrated architecture. We achieve a discrepancy of less than 2% between designed and measured frequencies for 6-GHz resonators. We also propose a design method that reduces the sensitivity of the resonant frequency to variations in the interchip spacing.
|
|
| 12. |
- Renberg Nilsson, Hampus, 1993, et al.
(författare)
-
High-Gain Traveling-Wave Parametric Amplifier Based on Three-Wave Mixing
- 2023
-
Ingår i: Physical Review Applied. - 2331-7019. ; 19:4
-
Tidskriftsartikel (refereegranskat)abstract
- We extend the theory for a Josephson-junction traveling-wave parametric amplifier (TWPA) operat-ing in the three-wave-mixing regime and we propose a scheme for achieving high gain. The continuous three-mode model [P.K. Tien, J. Appl. Phys. 29, 1347 (1958)] is, on one hand, extended to describe a discrete chain of Josephson junctions at high frequencies close to the spectral cutoff where there is no up -conversion. On the other hand, we also develop a continuous multimode theory for the small frequency limit where the frequency dispersion is close to linear. We find that in both cases the gain is significantly reduced compared to the prediction by the continuous three-mode model as the result of increasingly strong dispersion at the high frequencies and generation of up-converted modes at the small frequencies. The developed theory is in quantitative agreement with simulations of the full solution of the dynamical equations. To recover the high gain, we propose to engineer a chain with dispersive features to form a two-band frequency spectrum and to place the pump frequency within the upper band close to the spectral cutoff. We prove that there exists a sweet spot, where the signal and the pump are phase matched, while the up-conversion is inhibited. This results in a high gain, which grows exponentially with the length of the TWPA.
|
|
| 13. |
- Renberg Nilsson, Hampus, 1993, et al.
(författare)
-
Peripheral circuits for ideal performance of a traveling-wave parametric amplifier
- 2024
-
Ingår i: Physical Review Applied. - 2331-7019. ; 21:6
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the peripheral circuits required to enable ideal performance for a high-gain traveling-wave parametric amplifier (TWPA) based on three-wave mixing. By embedding the TWPA in a network of superconducting diplexers, hybrid couplers, and impedance matching networks, the amplifier can deliver a high stable gain with near-quantum-limited noise performance, with suppressed gain ripples, while eliminating the reflections of the signal, the idler and the pump as well as the transmission of all unwanted tones. We also demonstrate a configuration where the amplifier can isolate. We call this technique wideband idler filtering (WIF). The theory is supported by simulations that predict over 20 dB gain in the 4-8 GHz band with 10 dB isolation for a single amplifier and 30 dB isolation for two cascaded amplifiers. We demonstrate how the WIF-TWPAs can be used to construct controllable isolators with over 40 dB isolation over the full 4-8 GHz band. Finally, we look at nonidealities and show how certain nonidealities can be devastating for both the gain and the idler filtering, especially a cutoff imbalance or a flux imbalance, and discuss how to compensate for them.
|
|
| 14. |
- Shekarforoush, Sima, et al.
(författare)
-
Enhanced nonlinear optical susceptibilities in phosphorene nanoribbons: Ab initio study
- 2018
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 123:24
-
Tidskriftsartikel (refereegranskat)abstract
- Using density functional theory method, the linear optical absorption spectra and nonlinear optical susceptibilities of hydrogen passivated armchair and zigzag Phosphorous Nanoribbons (aPNR and zPNR) as well as α-phase phosphorous monolayer were calculated. It was observed that the crystallographic direction has a strong effect on the band edge absorption which in turn leads to optical anisotropy as well as a red shift of the absorption spectra by increasing the width. The calculated absorption values are in the order of 105cm-1and are very close to the experimentally measured ones. It was also observed that the 2nd order nonlinear optical susceptibility, χ(2), in the nanoribbons is enhanced by two orders of magnitude. This effect is caused by breaking the centro-symmetric structure of monolayer phosphorene as a result of hydrogen surface termination. The calculated 3rd order susceptibilities, χ(3), are in the order of ≈10-13esu (≈10-21m2/V2) which are in close agreement with experimentally reported values as well as those computed based on the relativistic picture of electron. The closeness of our results to experimental values strongly supports the reliability of our method in calculating the nonlinear optical susceptibilities of phosphorene and other nanostructures in general. The enhanced 2nd order optical nonlinearity in phosphorene promises a better second harmonic and frequency difference (THz) generation.
|
|
| 15. |
- Shekarforoush, Sima, et al.
(författare)
-
Optical transitions and localized edge states in skewed zigzag phosphorene nanoribbons
- 2018
-
Ingår i: Materials Express. - : American Scientific Publishers. - 2158-5857 .- 2158-5849. ; 8:6, s. 489-499
-
Tidskriftsartikel (refereegranskat)abstract
- Using the Tight Binding (TB) parameters extracted from Density Functional Theory (DFT) and Recursive Green's Function method (RGF), it is shown that skewed-zigzag black phosphorus (phosphorene) nanoribbons obtain large and tuneable bandgap in response to vertical and transverse electric fields. Depending on the direction of the applied field the mid-gap states could possess the localized or metallic nature i.e., non-zero midgap density of states. Adjustability of the bandgap and optical dipole transition matrix elements are explained based on the symmetry of involved band edge states. This promises new electronic and optical devices based on phosphorene nanoribbons.
|
|
| 16. |
- Shiri, Daryoush, 1975, et al.
(författare)
-
Photo absorption enhancement in strained silicon nanowires: An atomistic study
- 2017
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 122:3
-
Tidskriftsartikel (refereegranskat)abstract
- The absorption spectra of silicon nanowires are calculated using semi-empirical sp(3) d(5) s* tight binding and Density Functional Theory methods. The roles of diameter, wave function symmetry, strain, and crystallographic direction in determining the absorption are discussed. We find that compressive strain can change the band edge absorption by more than one order of magnitude due to the change in wave function symmetry. In addition, photon polarization with respect to the nanowire axis significantly alters the band edge absorption. Overall, the band edge absorption of [ 110] and [100] silicon nanowires can differ by as much as three orders of magnitude. We find that compared to bulk Silicon, a strained Silicon nanowire array can absorb infrared photons (1.1 eV) approximately one hundred times better. Finally, we compare a fully numerical and a computationally efficient semi-analytical method, and find that they both yield satisfactory values of the band edge absorption.
|
|
| 17. |
- Verma, Amit, et al.
(författare)
-
Low-Temperature Effects on Electron Transport in Small-Diameter Silicon Nanowire
- 2023
-
Ingår i: 2023 IEEE Nanotechnology Materials and Devices Conference (NMDC). - 9798350335460 ; , s. 31-34
-
Konferensbidrag (refereegranskat)abstract
- We report on modeling studies on the effect of very low temperatures (4K-77K) on the behavior of electron transport in a [110] axially aligned, 1.3 nm diameter unstrained silicon nanowire (SiNW). A sp3d5s * tight-binding scheme is used to calculate the band structure within an Ensemble Monte Carlo simulation. Electron scattering occurs through bulk-acoustic and bulk-optical phonons and includes intra-subband and inter-subband events. A comparison with room temperature (300K) shows that at lower temperatures, average electron steady-state drift velocity increases by 2 or more times at relatively moderate electric fields. Transient average electron velocity also shows a more pronounced streaming motion. This is attributed to an overall decrease in electron-phonon scattering rates with temperature.
|
|
