Cryogenic Amplification Research Articles

Recent Developments in Quantum‐Circuit Refrigeration

AbstractThe recent progress in direct active cooling of the quantum‐electric degrees of freedom in engineered circuits, or quantum‐circuit refrigeration is reviewed. In 2017, the discovery of a quantum‐circuit refrigerator (QCR) based on photon‐assisted tunneling of quasiparticles through normal‐metal–insulator–superconductor junctions inspired a series of experimental studies demonstrating the following main properties: i) the direct‐current (dc) bias voltage of the junction can change the QCR‐induced damping rate of a superconducting microwave resonator by orders of magnitude and give rise to nontrivial Lamb shifts, ii) the damping rate can be controlled in nanosecond time scales, and ii) the dc bias can be replaced by a microwave excitation, the amplitude of which controls the induced damping rate. Theoretically, it is predicted that state‐of‐the‐art superconducting resonators and qubits can be reset with an infidelity lower than 10−4 in tens of nanoseconds using experimentally feasible parameters. A QCR‐equipped resonator has also been demonstrated as an incoherent photon source with an output temperature above 1 K yet operating at millikelvin. This source has been used to calibrate cryogenic amplification chains. In the future, the QCR may be experimentally used to quickly reset superconducting qubits, and hence assist in the great challenge of building a practical quantum computer.

Cryogenic amplification of image-charge detection for readout of quantum states of electrons on liquid helium

Accurate detection of quantum states is a vital step in the development of quantum computing. Image-charge detection of quantum states of electrons on liquid helium can potentially be used for the readout of a single-electron qubit; however, low sensitivity due to added noise hinders its usage in high fidelity and bandwidth (BW) applications. One method to improve the readout accuracy and bandwidth is to use cryogenic amplifications near the signal source to minimize the effects of stray capacitance. We experimentally demonstrate a two-stage amplification scheme with a low power dissipation of 90 {\mu}W at the first stage located at the still plate of the dilution refrigerator and a high gain of 40 dB at the second stage located at the 4 K plate. The good impedance matching between different stages and output devices ensure high BW and constant gain in a wide frequency range. The detected image-charge signals are compared for one-stage and two-stage amplification schemes.

Transformer-Coupled TES Frequency Domain Readout Prototype

Frequency-domain multiplexing (fMUX) is a mature readout scheme for transition edge sensor (TES) detectors in the millimetre and sub-millimetre bands. It is implemented at MHz carrier frequencies for the South Pole Telescope, POLARBEAR, and Simons Array and is planned for deployment on the LiteBIRD space polarimeter. The existing implementations couple to the detectors with low-noise, low-input-impedance superconducting quantum interference device (SQUID) transimpedance amplifiers and rely on complex arrangements to achieve sufficient linearity and dynamic range. We introduce a new cryogenic amplification scheme that couples the multiplexed TES devices to a traditional, high-linearity, high-dynamic-range, field-effect transistor amplifier using a novel high-turns-ratio, wide-band cryogenic transformer. We characterize the bandwidth, transimpedance, input impedance, and system noise of the transformer-coupled fMUX system to demonstrate that it is a promising candidate for MHz frequency-domain multiplexing without the use of SQUIDs. For the initial prototype, we demonstrate a bandwidth of 1.5–6 MHz, transimpedance of $$267 \pm 2 \,{\Omega}$$, input impedance of $$0.2\,{\Omega}$$, and system noise $$16 \pm 3\,{\mathrm {pA}}/\sqrt{{\mathrm {Hz}}}$$. We also present an optimized design which will have amplifier noise contributions of approximately $$5 \,{\mathrm {pA}}/\sqrt{{\mathrm {Hz}}}$$, comparable to the SQUID contribution in the existing systems.

Single-Shot Readout Performance of Two Heterojunction-Bipolar-Transistor Amplification Circuits at Millikelvin Temperatures

High-fidelity single-shot readout of spin qubits requires distinguishing states much faster than the T1 time of the spin state. One approach to improving readout fidelity and bandwidth (BW) is cryogenic amplification, where the signal from the qubit is amplified before noise sources are introduced and room-temperature amplifiers can operate at lower gain and higher BW. We compare the performance of two cryogenic amplification circuits: a current-biased heterojunction bipolar transistor circuit (CB-HBT), and an AC-coupled HBT circuit (AC-HBT). Both circuits are mounted on the mixing-chamber stage of a dilution refrigerator and are connected to silicon metal oxide semiconductor (Si-MOS) quantum dot devices on a printed circuit board (PCB). The power dissipated by the CB-HBT ranges from 0.1 to 1 μW whereas the power of the AC-HBT ranges from 1 to 20 μW. Referred to the input, the noise spectral density is low for both circuits, in the 15 to 30 fA/sqrt{{bf{Hz}}} range. The charge sensitivity for the CB-HBT and AC-HBT is 330 μe/sqrt{{bf{Hz}}} and 400 μe/sqrt{{bf{Hz}}}, respectively. For the single-shot readout performed, less than 10 μs is required for both circuits to achieve bit error rates below 10−3, which is a putative threshold for quantum error correction.

Calibration of cryogenic amplification chains using normal-metal–insulator–superconductor junctions

Various applications of quantum devices call for an accurate calibration of cryogenic amplification chains. To this end, we present an experimentally feasible calibration scheme and use it to accurately measure the total gain and noise temperature of an amplification chain by employing normal-metal–insulator–superconductor (NIS) junctions. Our method is based on the radiation emitted by inelastic electron tunneling across voltage-biased NIS junctions. We derive an analytical expression that relates the generated power to the applied bias voltage which is the only control parameter of the device. After the setup has been characterized using a standard voltage reflection measurement, the total gain and the noise temperature are extracted by fitting the analytical expression to the microwave power measured at the output of the amplification chain. The 1σ uncertainty of the total gain of 51.84 dB appears to be of the order of 0.10 dB.

Low-noise correlation measurements based on software-defined-radio receivers and cooled microwave amplifiers.

We present a microwave correlation measurement system based on two low-cost USB-connected software defined radio dongles modified to operate as coherent receivers by using a common local oscillator. Existing software is used to obtain I/Q samples from both dongles simultaneously at a software tunable frequency. To achieve low noise, we introduce an easy low-noise solution for cryogenic amplification at 600-900 MHz based on single discrete HEMT with 21 dB gain and 7 K noise temperature. In addition, we discuss the quantization effects in a digital correlation measurement and determination of optimal integration time by applying Allan deviation analysis.

Front-end system for Yb : YAG cryogenic disk laser

A new front-end system for a cryogenic Yb : YAG laser is designed. The system consists of a femtosecond source, a stretcher and a regenerative amplifier with an output energy of at a pulse repetition rate of , a pulse duration of and a bandwidth of . After increasing the pump power of the regenerative amplifier, it is expected to achieve a pulse energy of at the input to cryogenic amplification stages, which will allow one to obtain laser pulses with a duration of several picoseconds at the output of the cryogenic laser after compression.

Induction-detection electron spin resonance with sensitivity of 1000 spins: En route to scalable quantum computations

The detection and imaging with high spatial resolution of a small number of electron spins is an important problem in science and technology. Here we show that, by making use of the smallest electron spin resonance resonator constructed to date (∼5μm) together with a unique cryogenic amplification scheme and submicron imaging capabilities, a sensitivity of less than 1000 electron spins is obtained with spatial resolution of ∼500 nm. This is the most sensitive induction-detection experiment carried out to date and it opens the door to many potential applications, one of which is the demonstration of a scalable quantum computation capability.

Dc SQUIDs as linear displacement detectors for embedded micromechanical resonators

Abstract Superconducting quantum interference devices (SQUIDs) can detect tiny amounts of magnetic flux and are also used to study macroscopic quantum effects. We employ a dc SQUID as a linear detector of the displacement of an embedded micromechanical resonator with a femtometer sensitivity. We discuss the measurement method, including operation in high magnetic field and a cryogenic amplification scheme which allows us to reach a resolution which is only a factor 4.4 above the standard quantum limit.

System for measuring auto- and cross correlation of current noise at low temperatures

We describe the construction and operation of a two-channel noise detection system for measuring power and cross spectral densities of current fluctuations near 2MHz in electronic devices at low temperatures. The system employs cryogenic amplification and fast Fourier transform based spectral measurement. The gain and electron temperature are calibrated using Johnson noise thermometry. Full shot noise of 100pA can be resolved with an integration time of 10s. We report a demonstration measurement of bias-dependent current noise in a gate defined GaAs∕AlGaAs quantum point contact.

Cryogenic amplification system for ultra-low noise measurements

We present a low-cost ultra-low-noise cryogenic amplifier, which has been developed for the investigation of shot noise suppression and enhancement in double-barrier resonant-tunneling devices. Results of the noise measurements performed on the amplifier operating at liquid nitrogen temperature are discussed and compared to those obtained at room temperature.