| 11. |
- Li, Hangxi, 1994, et al.
(författare)
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Experimentally Verified, Fast Analytic, and Numerical Design of Superconducting Resonators in Flip-Chip Architectures
- 2023
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Ingår i: IEEE Transactions on Quantum Engineering. ; 4
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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.
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| 12. |
- Renberg Nilsson, Hampus, 1993, et al.
(författare)
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High-Gain Traveling-Wave Parametric Amplifier Based on Three-Wave Mixing
- 2023
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Ingår i: Physical Review Applied. - 2331-7019. ; 19:4
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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.
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| 13. |
- Shekarforoush, Sima, et al.
(författare)
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Enhanced nonlinear optical susceptibilities in phosphorene nanoribbons: Ab initio study
- 2018
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 123:24
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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.
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| 14. |
- Shekarforoush, Sima, et al.
(författare)
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Optical transitions and localized edge states in skewed zigzag phosphorene nanoribbons
- 2018
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Ingår i: Materials Express. - : American Scientific Publishers. - 2158-5857 .- 2158-5849. ; 8:6, s. 489-499
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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.
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| 15. |
- Shiri, Daryoush, 1975, et al.
(författare)
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Photo absorption enhancement in strained silicon nanowires: An atomistic study
- 2017
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 122:3
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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.
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| 16. |
- Verma, Amit, et al.
(författare)
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Low-Temperature Effects on Electron Transport in Small-Diameter Silicon Nanowire
- 2023
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Ingår i: 2023 IEEE Nanotechnology Materials and Devices Conference (NMDC). - 9798350335460 ; , s. 31-34
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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.
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