28 research outputs found
Active Initialization Experiment of Superconducting Qubit Using Quantum-circuit Refrigerator
The initialization of superconducting qubits is one of the essential
techniques for the realization of quantum computation. In previous research,
initialization above 99\% fidelity has been achieved at 280 ns. Here, we
demonstrate the rapid initialization of a superconducting qubit with a
quantum-circuit refrigerator (QCR). Photon-assisted tunneling of quasiparticles
in the QCR can temporally increase the relaxation time of photons inside the
resonator and helps release energy from the qubit to the environment.
Experiments using this protocol have shown that 99\% of initialization time is
reduced to 180 ns. This initialization time depends strongly on the relaxation
rate of the resonator, and faster initialization is possible by reducing the
resistance of the QCR, which limits the ON/OFF ratio, and by strengthening the
coupling between the QCR and the resonator
Structural changes induced by electric currents in a single crystal of PrCuO
We demonstrate a novel approach to the structural and electronic property
modification of perovskites, focusing on PrCuO, an undoped parent
compound of a class of electron-doped copper-oxide superconductors. Currents
were passed parallel or perpendicular to the copper-oxygen layers with the
voltage ramped up until a rapid drop in the resistivity was achieved, a process
referred to as "flash". The current was then further increased tenfold in
current-control mode. This state was quenched by immersion into liquid
nitrogen. Flash can drive many compounds into different atomic structures with
new properties, whereas the quench freezes them into a long-lived state.
Single-crystal neutron diffraction of as-grown and modified PrCuO
revealed a x superlattice due to oxygen-vacancy order.
The diffraction peak intensities of the superlattice of the modified sample
were significantly enhanced relative to the pristine sample. Raman-active
phonons in the modified sample were considerably sharper. Measurements of
electrical resistivity, magnetization and two-magnon Raman scattering indicate
that the modification affected only the Pr-O layers, but not the Cu-O planes.
These results point to enhanced oxygen-vacancy order in the modified samples
well beyond what can be achieved without passing electrical current. Our work
opens a new avenue toward electric field/quench control of structure and
properties of layered perovskite oxides
On-Demand Single-Electron Source via Single-Cycle Acoustic Pulses
Surface acoustic waves (SAWs) are a reliable solution to transport single
electrons with precision in piezoelectric semiconductor devices. Recently,
highly efficient single-electron transport with a strongly compressed
single-cycle acoustic pulse has been demonstrated. This approach, however,
requires surface gates constituting the quantum dots, their wiring, and
multiple gate movements to load and unload the electrons, which is very
time-consuming. Here, on the contrary, we employ such a single-cycle acoustic
pulse in a much simpler way - without any quantum dot at the entrance or exit
of a transport channel - to perform single-electron transport between distant
electron reservoirs. We observe the transport of a solitary electron in a
single-cycle acoustic pulse via the appearance of the quantized
acousto-electric current. The simplicity of our approach allows for on-demand
electron emission with arbitrary delays on a ns time scale. We anticipate that
enhanced synthesis of the SAWs will facilitate electron-quantum-optics
experiments with multiple electron flying qubits
Generation of a single-cycle acoustic pulse: a scalable solution for transport in single-electron circuits
The synthesis of single-cycle, compressed optical and microwave pulses
sparked novel areas of fundamental research. In the field of acoustics,
however, such a generation has not been introduced yet. For numerous
applications, the large spatial extent of surface acoustic waves (SAW) causes
unwanted perturbations and limits the accuracy of physical manipulations.
Particularly, this restriction applies to SAW-driven quantum experiments with
single flying electrons, where extra modulation renders the exact position of
the transported electron ambiguous and leads to undesired spin mixing. Here, we
address this challenge by demonstrating single-shot chirp synthesis of a
strongly compressed acoustic pulse. Employing this solitary SAW pulse to
transport a single electron between distant quantum dots with an efficiency
exceeding 99%, we show that chirp synthesis is competitive with regular
transduction approaches. Performing a time-resolved investigation of the
SAW-driven sending process, we outline the potential of the chirped SAW pulse
to synchronize single-electron transport from many quantum-dot sources. By
superimposing multiple pulses, we further point out the capability of chirp
synthesis to generate arbitrary acoustic waveforms tailorable to a variety of
(opto)nanomechanical applications. Our results shift the paradigm of compressed
pulses to the field of acoustic phonons and pave the way for a SAW-driven
platform of single-electron transport that is precise, synchronized, and
scalable.Comment: To be published in Physical Review
Interplay of the Inverse Proximity Effect and Magnetic Field in Out-of-Equilibrium Single-Electron Devices
We show that a weak external magnetic field affects significantly nonequilibrium quasiparticle (QP) distributions under the conditions of the inverse proximity effect, using the single-electron hybrid turnstile as a generic example. Inverse proximity suppresses the superconducting gap in superconducting leads in the vicinity of turnstile junctions, thus, trapping hot QPs in this region. An external magnetic field creates additional QP traps in the leads in the form of vortices or regions with a reduced superconducting gap resulting in the release of QPs away from the junctions. We present clear experimental evidence of the interplay of the inverse proximity effect and magnetic field revealing itself in the superconducting gap enhancement and significant improvement of the turnstile characteristics. The observed interplay and its theoretical explanation in the context of QP overheating are important for various superconducting and hybrid nanoelectronic devices, which find applications in quantum computation, photon detection, and quantum metrology