Interference effects in a tunable quantum point contact integrated with an electronic cavity

We show experimentally how quantum interference can be produced using an integrated quantum system comprising an arch-shaped short quantum wire (or quantum point contact, QPC) of 1D electrons and a reflector forming an electronic cavity. On tuning the coupling between the QPC and the electronic cavity, fine oscillations are observed when the arch QPC is operated in the quasi-1D regime. These oscillations correspond to interference between the 1D states and a state which is similar to the Fabry-Perot state and suppressed by a small transverse magnetic field of ±60  mT. Tuning the reflector, we find a peak in resistance which follows the behavior expected for a Fano resonance. We suggest that this is an interesting example of a Fano resonance in an open system which corresponds to interference at or near the Ohmic contacts due to a directly propagating, reflected discrete path and the continuum states of the cavity corresponding to multiple scattering. Remarkably, the Fano factor shows an oscillatory behavior taking peaks for each fine oscillation, thus, confirming coupling between the discrete and continuum states. The results indicate that such a simple quantum device can be used as building blocks to create more complex integrated quantum circuits for possible applications ranging from quantum-information processing to realizing the fundamentals of complex quantum systems

Stabilization of single-electron pumps by high magnetic fields

We study the effect of perpendicular magnetic fields on a single-electron system with a strongly time-dependent electrostatic potential. Continuous improvements to the current quantization in these electron pumps are revealed by high-resolution measurements. Simulations show that the sensitivity of tunnel rates to the barrier potential is enhanced, stabilizing particular charge states. Nonadiabatic excitations are also suppressed due to a reduced sensitivity of the Fock-Darwin states to electrostatic potential. The combination of these effects leads to significantly more accurate current quantization

Time-resolved Coulomb collision of single electrons

Precise control over interactions between ballistic electrons will enable us to exploit Coulomb interactions in novel ways, to develop high-speed sensing, to reach a non-linear regime in electron quantum optics and to realise schemes for fundamental two-qubit operations on flying electrons. Time-resolved collisions between electrons have been used to probe the indistinguishability, Wigner function and decoherence of single electron wavepackets. Due to the effects of screening, none of these experiments were performed in a regime where Coulomb interactions were particularly strong. Here we explore the Coulomb collision of two high energy electrons in counter-propagating ballistic edge states. We show that, in this kind of unscreened device, the partitioning probabilities at different electron arrival times and barrier height are shaped by Coulomb repulsion between the electrons. This prevents the wavepacket overlap required for the manifestation of fermionic exchange statistics but suggests a new class of devices for studying and manipulating interactions of ballistic single electrons

Nonequilibrium phenomena in bilayer electron systems

In the present Letter, we have used magnetocapacitance and magnetoresistance measurements to investigate nonequilibrium phenomena in a bilayer electron system based on GaAs/AlGaAs heterostructures. The magnetic field ramping drives the bilayer electron system out of equilibrium, leading to magnetoresistance hysteresis and spikes. Unlike magnetoresistance, magnetocapacitance results intriguingly show hysteresis even when both layers are in the quantum Hall state. The hysteresis is accompanied by interlayer charge transfer, but the disequilibrium is not limited to interlayer imbalance. Results show that the edge-bulk imbalance can be the initial ground for the appearance of hysteresis. In addition, the nonequilibrium states are observed in which the total, rather than individual, layer densities determine the magnetic field and gate voltage dependencies

Formation and evolution of cosmic D-strings

We study the formation of D and F-cosmic strings in D-brane annihilation after brane inflation. We show that D-string formation by quantum de Sitter fluctuations is severely suppressed, due to suppression of RR field fluctuations in compact dimensions. We discuss the resonant mechanism of production of D and F-strings, which are formed as magnetic and electric flux tubes of the two orthogonal gauge fields living on the world-volume of the unstable brane. We outline the subsequent cosmological evolution of the D-F string network. We also compare the nature of these strings with the ordinary cosmic strings and point out some differences and similarities.Comment: Added discussion and reference

Incipient singlet-triplet states in a hybrid mesoscopic system

In the present Rapid Communication, we provide an easily accessible way to achieve the singlet-triplet Kondo effect in a hybrid system consisting of a quantum point contact (QPC) coupled to an electronic cavity. We show that by activating the coupling between the QPC and cavity, a zero-bias anomaly occurs in a low conductance regime, a coexistence of a zero-bias and finite-bias anomaly (FBA) in a medium conductance regime, and a FBA-only anomaly in a high conductance regime. The latter two observations are due to the singlet-triplet Kondo effect