25 research outputs found
Voltage-Controlled Superconducting Quantum Bus
We demonstrate the ability of an epitaxial semiconductor-superconductor
nanowire to serve as a field-effect switch to tune a superconducting cavity.
Two superconducting gatemon qubits are coupled to the cavity, which acts as a
quantum bus. Using a gate voltage to control the superconducting switch yields
up to a factor of 8 change in qubit-qubit coupling between the on and off
states without detrimental effect on qubit coherence. High-bandwidth operation
of the coupling switch on nanosecond timescales degrades qubit coherence
Anharmonicity of a Gatemon Qubit with a Few-Mode Josephson Junction
Coherent operation of gate-voltage-controlled hybrid transmon qubits
(gatemons) based on semiconductor nanowires was recently demonstrated. Here we
experimentally investigate the anharmonicity in epitaxial InAs-Al Josephson
junctions, a key parameter for their use as a qubit. Anharmonicity is found to
be reduced by roughly a factor of two compared to conventional metallic
junctions, and dependent on gate voltage. Experimental results are consistent
with a theoretical model, indicating that Josephson coupling is mediated by a
small number of highly transmitting modes in the semiconductor junction
Suppressed Charge Dispersion via Resonant Tunneling in a Single-Channel Transmon
We demonstrate strong suppression of charge dispersion in a
semiconductor-based transmon qubit across Josephson resonances associated with
a quantum dot in the junction. On resonance, dispersion is drastically reduced
compared to conventional transmons with corresponding Josephson and charging
energies. We develop a model of qubit dispersion for a single-channel
resonance, which is in quantitative agreement with experimental data
A Parity-Protected Superconductor-Semiconductor Qubit
Coherence of superconducting qubits can be improved by implementing designs
that protect the parity of Cooper pairs on superconducting islands. Here, we
introduce a parity-protected qubit based on voltage-controlled semiconductor
nanowire Josephson junctions, taking advantage of the higher harmonic content
in the energy-phase relation of few-channel junctions. A symmetric
interferometer formed by two such junctions, gate-tuned into balance and
frustrated by a half-quantum of applied flux, yields a cos(2{\phi}) Josephson
element, reflecting coherent transport of pairs of Cooper pairs. We demonstrate
that relaxation of the qubit can be suppressed tenfold by tuning into the
protected regime
Gate-Tunable Transmon Using Selective-Area-Grown Superconductor-Semiconductor Hybrid Structures on Silicon
We present a gate-voltage tunable transmon qubit (gatemon) based on planar
InAs nanowires that are selectively grown on a high resistivity silicon
substrate using III-V buffer layers. We show that low loss superconducting
resonators with an internal quality of can readily be realized
using these substrates after the removal of buffer layers. We demonstrate
coherent control and readout of a gatemon device with a relaxation time,
, and dephasing times, and .
Further, we infer a high junction transparency of from an analysis
of the qubit anharmonicity
Quantum coherent control of a hybrid superconducting circuit made with graphene-based van der Waals heterostructures
Quantum coherence and control is foundational to the science and engineering
of quantum systems. In van der Waals (vdW) materials, the collective coherent
behavior of carriers has been probed successfully by transport measurements.
However, temporal coherence and control, as exemplified by manipulating a
single quantum degree of freedom, remains to be verified. Here we demonstrate
such coherence and control of a superconducting circuit incorporating
graphene-based Josephson junctions. Furthermore, we show that this device can
be operated as a voltage-tunable transmon qubit, whose spectrum reflects the
electronic properties of massless Dirac fermions traveling ballistically. In
addition to the potential for advancing extensible quantum computing
technology, our results represent a new approach to studying vdW materials
using microwave photons in coherent quantum circuits