| 1. |
- Shiri, Daryoush, 1975, et al.
(författare)
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An Electrically Controlled Heat Rectifier using Graphene Nanoribbons
- 2019
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Ingår i: 2019 IEEE 14th Nanotechnology Materials and Devices Conference, NMDC 2019. - 2378-377X. - 9781728126371 ; October 2019, s. 1-4
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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.
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| 2. |
- Shiri, Daryoush, 1975, et al.
(författare)
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Gunn-Hilsum Effect in Mechanically Strained Silicon Nanowires: Tunable Negative Differential Resistance
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 8:1
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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.
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| 3. |
- Shiri, Daryoush, 1975, et al.
(författare)
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Heat-to-mechanical energy conversion in graphene: Manifestation of Umklapp enhancement with strain
- 2019
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 125:12
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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.
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| 4. |
- Anantram, M. P., et al.
(författare)
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Quantum Mechanics for Engineers and Material Scientists: An Introduction
- 2024
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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.
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| 5. |
- 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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| 6. |
- Bengtsson, Andreas, 1991, et al.
(författare)
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Improved Success Probability with Greater Circuit Depth for the Quantum Approximate Optimization Algorithm
- 2020
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Ingår i: Physical Review Applied. - 2331-7019. ; 14:3
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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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| 7. |
- Fadavi Roudsari, Anita, 1978, et al.
(författare)
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Three-wave mixing traveling-wave parametric amplifier with periodic variation of the circuit parameters
- 2023
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 122:5
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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.
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| 8. |
- Grigoras, K., et al.
(författare)
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Qubit-Compatible Substrates With Superconducting Through-Silicon Vias
- 2022
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Ingår i: IEEE Transactions on Quantum Engineering. - 2689-1808. ; 3
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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.
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| 9. |
- Islam, Shadli, et al.
(författare)
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Ab-initio Calculation of Nonlinear Optical Susceptibilities in Germanium Quantum Dots
- 2019
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Ingår i: 2018 IEEE 13TH NANOTECHNOLOGY MATERIALS AND DEVICES CONFERENCE (NMDC). - 2378-377X. - 9781538610169 ; , s. 113-116
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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.
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| 10. |
- Kosen, Sandoko, 1991, et al.
(författare)
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Building blocks of a flip-chip integrated superconducting quantum processor
- 2022
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Ingår i: Quantum Science and Technology. - : IOP Publishing. - 2058-9565. ; 7:3
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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.
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