Magnetotransport in an aluminum thin film on a GaAs substrate grown by molecular beam epitaxy

Magnetotransport measurements are performed on an aluminum thin film grown on a GaAs substrate. A crossover from electron- to hole-dominant transport can be inferred from both longitudinal resistivity and Hall resistivity with increasing the perpendicular magnetic field B. Also, phenomena of localization effects can be seen at low B. By analyzing the zero-field resistivity as a function of temperature T, we show the importance of surface scattering in such a nanoscale film

Time-resolved measurement of pulse-to-pulse heating effects in a terahertz quantum cascade laser using an NbN superconducting detector

Joule heating causes significant degradation in the power emitted from terahertz-frequency quantum-cascade lasers (THz QCLs). However, to date, it has not been possible to characterize the thermal equilibration time of these devices, since THz power degradation over sub-millisecond time-scales cannot be resolved using conventional bolometric or pyroelectric detectors. In this letter, we use a superconducting antenna-coupled niobium nitride detector to measure the emission from a THz QCL with a nanosecond-scale time-resolution. The emitted THz power is shown to decay more rapidly at higher heat-sink temperatures, and in steady-state the power reduces as the repetition rate of the driving pulses increases. The pulse-to-pulse variation in active-region temperature is inferred by comparing the THz signals with those obtained from low duty-cycle measurements. A thermal resistance of 8.2±0.6 K/W is determined, which is in good agreement with earlier measurements, and we calculate a 370±90-μs bulk heat-storage time, which corresponds to the simulated heat capacity of the device substrate

Magnetic vortices in superconducting photon detectors

We have measured critical-current densities in micro- and nanometer wide thin-film NbN bridges. These bridges show significant changes in the temperature dependence of the critical-current density depending on the strip width. Taking into account the boundary conditions at the strip edges we can qualitatively describe our data applying a geometric edge-barrier model. We conclude that sub-µm wide bridges remain free of single vortices in ambient magnetic fields and at currents up to the depairing critical-current density. This also means that NbN meanders of superconducting single photon detectors should be free of single vortices under normal operating conditions

Single-photon detectors for optical quantum information applications

The past decade has seen a dramatic increase in interest in new single-photon detector technologies. A major cause of this trend has undoubtedly been the push towards optical quantum information applications such as quantum key distribution. These new applications place extreme demands on detector performance that go beyond the capabilities of established single-photon detectors. There has been considerable effort to improve conventional photon-counting detectors and to transform new device concepts into workable technologies for optical quantum information applications. This Review aims to highlight the significant recent progress made in improving single-photon detector technologies, and the impact that these developments will have on quantum optics and quantum information science