7 research outputs found
Strong Microwave Squeezing Above 1 Tesla and 1 Kelvin
Squeezed states of light have been used extensively to increase the precision
of measurements, from the detection of gravitational waves to the search for
dark matter. In the optical domain, high levels of vacuum noise squeezing are
possible due to the availability of low loss optical components and
high-performance squeezers. At microwave frequencies, however, limitations of
the squeezing devices and the high insertion loss of microwave components makes
squeezing vacuum noise an exceptionally difficult task. Here we demonstrate a
new record for the direct measurement of microwave squeezing. We use an ultra
low loss setup and weakly-nonlinear kinetic inductance parametric amplifiers to
squeeze microwave noise 7.8(2) dB below the vacuum level. The amplifiers
exhibit a resilience to magnetic fields and permit the demonstration of record
squeezing levels inside fields of up to 2 T. Finally, we exploit the high
critical temperature of our amplifiers to squeeze a warm thermal environment,
achieving vacuum level noise at a temperature of 1.8 K. These results enable
experiments that combine squeezing with magnetic fields and permit
quantum-limited microwave measurements at elevated temperatures, significantly
reducing the complexity and cost of the cryogenic systems required for such
experiments.Comment: Main text: 9 pages, 4 figures. Supplementary information: 21 pages,
17 figure
Superconducting Gatemon Qubit based on a Proximitized Two-Dimensional Electron Gas
The coherent tunnelling of Cooper pairs across Josephson junctions (JJs)
generates a nonlinear inductance that is used extensively in quantum
information processors based on superconducting circuits, from setting qubit
transition frequencies and interqubit coupling strengths, to the gain of
parametric amplifiers for quantum-limited readout. The inductance is either set
by tailoring the metal-oxide dimensions of single JJs, or magnetically tuned by
parallelizing multiple JJs in superconducting quantum interference devices
(SQUIDs) with local current-biased flux lines. JJs based on
superconductor-semiconductor hybrids represent a tantalizing all-electric
alternative. The gatemon is a recently developed transmon variant which employs
locally gated nanowire (NW) superconductor-semiconductor JJs for qubit control.
Here, we go beyond proof-of-concept and demonstrate that semiconducting
channels etched from a wafer-scale two-dimensional electron gas (2DEG) are a
suitable platform for building a scalable gatemon-based quantum computer. We
show 2DEG gatemons meet the requirements by performing voltage-controlled
single qubit rotations and two-qubit swap operations. We measure qubit
coherence times up to ~2 us, limited by dielectric loss in the 2DEG host
substrate
Exploring the Semiconducting Josephson Junction of Nanowire-based Superconducting Qubits
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Latched detection of zeptojoule spin echoes with a kinetic inductance parametric oscillator.
When strongly pumped at twice their resonant frequency, nonlinear resonators develop a high-amplitude intracavity field, a phenomenon known as parametric self-oscillations. The boundary over which this instability occurs can be extremely sharp and thereby presents an opportunity for realizing a detector. Here, we operate such a device based on a superconducting microwave resonator whose nonlinearity is engineered from kinetic inductance. The device indicates the absorption of low-power microwave wavepackets by transitioning to a self-oscillating state. Using calibrated pulses, we measure the detection efficiency to zeptojoule energy wavepackets. We then apply it to measurements of electron spin resonance, using an ensemble of 209Bi donors in silicon that are inductively coupled to the resonator. We achieve a latched readout of the spin signal with an amplitude that is five hundred times greater than the underlying spin echoes
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In situ amplification of spin echoes within a kinetic inductance parametric amplifier
The use of superconducting microresonators together with quantum-limited Josephson parametric amplifiers has enhanced the sensitivity of pulsed electron spin resonance (ESR) measurements by more than four orders of magnitude. So far, the microwave resonators and amplifiers have been designed as separate components due to the incompatibility of Josephson junction-based devices with magnetic fields. This has produced complex spectrometers and raised technical barriers toward adoption of the technique. Here, we circumvent this issue by coupling an ensemble of spins directly to a weakly nonlinear and magnetic field-resilient superconducting microwave resonator. We perform pulsed ESR measurements with a 1-pL mode volume containing 6 × 107 spins and amplify the resulting signals within the device. When considering only those spins that contribute to the detected signals, we find a sensitivity of [Formula: see text] for a Hahn echo sequence at a temperature of 400 mK. In situ amplification is demonstrated at fields up to 254 mT, highlighting the technique's potential for application under conventional ESR operating conditions
Microwave sensing of Andreev bound states in a gate-defined superconducting quantum point contact
We use a superconducting microresonator as a cavity to sense absorption of
microwaves by a superconducting quantum point contact defined by surface gates
over a proximitized two-dimensional electron gas. Renormalization of the cavity
frequency with phase difference across the point contact is consistent with
adiabatic coupling to Andreev bound states. Near phase difference, we
observe random fluctuations in absorption with gate voltage, related to quantum
interference-induced modulations in the electron transmission. We identify
features consistent with the presence of single Andreev bound states and
describe the Andreev-cavity interaction using a dispersive Jaynes-Cummings
model. By fitting the weak Andreev-cavity coupling, we extract ~GHz decoherence
consistent with charge noise and the transmission dispersion associated with a
localized state
Destructive Little-Parks Effect in a Full-Shell Nanowire-Based Transmon
A semiconductor transmon with an epitaxial Al shell fully surrounding an InAs nanowire core is investigated in the low EJ/EC regime. Little-Parks oscillations as a function of flux along the hybrid wire axis are destructive, creating lobes of reentrant superconductivity separated by a metallic state at a half quantum of applied flux. In the first lobe, phase winding around the shell can induce topological superconductivity in the core. Coherent qubit operation is observed in both the zeroth and first lobes. Splitting of parity bands by coherent single-electron coupling across the junction is not resolved beyond line broadening, placing a bound on Majorana coupling, EM/h<10 MHz, much smaller than the Josephson coupling EJ/h∼4.7 GHz.QRD/Kouwenhoven La