| 1. |
- 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
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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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| 2. |
- 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
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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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| 3. |
- 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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| 4. |
- 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
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Ingår i: Physical Review Applied. - 2331-7019. ; 15:4
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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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| 5. |
- Golubev, Dmitry, et al.
(författare)
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Single-Photon Detection with a Josephson Junction Coupled to a Resonator
- 2021
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Ingår i: Physical Review Applied. - 2331-7019. ; 16:1
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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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| 6. |
- Kunakova, Gunta, 1987, et al.
(författare)
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High-Mobility Ambipolar Magnetotransport in Topological Insulator Bi2Se3 Nanoribbons
- 2021
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Ingår i: Physical Review Applied. - 2331-7019. ; 16:2
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Tidskriftsartikel (refereegranskat)abstract
- Nanoribbons of topological insulators (TIs) have been suggested for a variety of applications exploiting the properties of the topologically protected surface Dirac states. In these proposals it is crucial to achieve a high tunability of the Fermi energy, through the Dirac point while preserving a high mobility of the involved carriers. Tunable transport in TI nanoribbons has been achieved by chemical doping of the materials so to reduce the bulk carriers' concentration, however at the expense of the mobility of the surface Dirac electrons, which is substantially reduced. Here we study bare Bi2Se3 nanoribbons transferred on a variety of oxide substrates and demonstrate that the use of a large relative permittivity SrTiO3 substrate enables the Fermi energy to be tuned through the Dirac point and an ambipolar field effect to be obtained. Through magnetotransport and Hall conductance measurements, performed on single Bi2Se3 nanoribbons, we demonstrate that electron and hole carriers are exclusively high-mobility Dirac electrons, without any bulk contribution. The use of SrTiO3 allows therefore an easy field effect gating in TI nanostructures providing an ideal platform to take advantage of the properties of topological surface states.
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| 7. |
- Lachmann, Sagy, et al.
(författare)
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Statistical Analysis of Field-Emission Currents
- 2021
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Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 16:2
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Tidskriftsartikel (refereegranskat)abstract
- The current due to cold tunneling of electrons from a metallic surface exposed to high electric fields, regularly named "dark current," is commonly described in modern literature using an analytical approximate solution provided by Murphy and Good [Phys. Rev. 102, 1464 (1956)]. This expression, which corrects earlier work by Fowler and Nordheim, is a Fowler-Nordheim-type equation: I similar to E2 exp(-a/E), where I is the dark current, E is the local electric field, and a is a system-specific constant. In this paper, a numerical approximation, rather than the analytical one given by Murphy and Good, is presented. This approximation is accurate over a wide range of fields, and is used to derive the effective field enhancement factor ,B. On the basis of this approximation, and considering local field and current fluctuations, two alternative methods for ,B estimation are presented. These methods allow instantaneous field-specific estimation of ,B, rather than the average estimate derived with current methods. The applicability of fluctuation-based methods is demonstrated by numerical simulation in a variety of conditions. The methods are applied to estimate ,B using fluctuation analysis in experimental measurements that were not dedicated for this purpose. An open-source code for the implementation of fluctuation-derived ,B estimation is provided, with an analysis of possible future experimental opportunities using dedicated experiments.
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| 8. |
- Litvinenko, A., et al.
(författare)
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Tunable Magnetoacoustic Oscillator with Low Phase Noise
- 2021
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Ingår i: Physical Review Applied. - 2331-7019. ; 15:3
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Tidskriftsartikel (refereegranskat)abstract
- A frequency-tunable low-phase-noise magnetoacoustic resonator is developed on the base of a parallel plate straight-edge bilayer consisting of an yttrium-iron-garnet (YIG) layer grown on a substrate of a gallium gadolinium garnet (GGG). When a YIG-GGG sample forms an ideal parallel plate, it supports a series of high-quality-factor acoustic modes standing along the plate thickness. Due to the magnetostriction of the YIG layer the ferromagnetic resonance (FMR) mode of the YIG layer can strongly interact with the acoustic thickness modes of the YIG-GGG structure, when the modes' frequencies match. A particular acoustic thickness mode used for the resonance excitations of the hybrid magnetoacoustic oscillations in a YIG-GGG bilayer is chosen by the YIG-layer FMR frequency, which can be tuned by the variation of the external bias magnetic field. A composite scheme of a magnetoacoustic oscillator, which includes a FMR-based resonance preselector, is developed to guarantee satisfaction of the Barkhausen criteria for a single-acoustic-mode oscillation regime. The developed low-phase-noise composite magnetoacoustic oscillator can be tuned from 0.84 to 1 GHz with an increment of about 4.773 MHz (frequency distance between the adjacent acoustic thickness modes in a YIG-GGG parallel plate), and demonstrates the phase noise of & minus;116 dBc/Hz at the offset frequency of 10 kHz.
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