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arXiv:2311.04437 · Journal of Low Temperature Physics

Cryogenic Resonant Amplifier for Electron-on-Helium Image Charge Readout

M. A. Belyanchikov, Jakob A. Kraus, Denis Konstantinov

Published Jan 19, 2024• 6 citations
arXivHTMLPDF

Abstract

Abstract An electron-on-helium qubit is a promising physical platform for quantum information technologies. Among all the “blueprints” for the qubit realization, a hybrid Rydberg-spin qubit seems to be a promising one toward quantum computing using electron spins. The main technological challenge on the way to such qubits is a detection of fA range image current induced by a Rydberg transition of a single electron. To address this problem, we aim to use a tank LC-circuit in conjunction with a high-impedance and low power dissipation cryogenic amplifier. Here, we report our progress toward realization of a resonant image current detector with a homemade cryogenic amplifier based on FHX13LG HEMT. We present a detailed characterization of the transistor at room and cryogenic temperatures, as well as details of the amplifier design and performance. At the power dissipation level of amplifier well below 100 μW, the measured voltage and current noise level are $$0.6~{\hbox {nV}}/\sqrt{\textrm{Hz}}$$ 0.6 nV / Hz and below 1.5 fA/ $$\sqrt{\textrm{Hz}}$$ Hz , respectively. Based on the actual image current measurements of the Rydberg transition in a many-electron system on liquid helium, we estimate an SNR = 8 with a measurement bandwidth 1 Hz for the detection of a single-electron transition, providing the noise level at the output is solely determined by the noise of the amplifier.

DOI
10.1007/s10909-023-03033-6

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We use a cryogenic high-electron-mobility transistor circuit to amplify the current from a single electron transistor, allowing for demonstration of single shot readout of an electron spin on a single P donor in Si with 100 kHz bandwidth and a signal to noise ratio of ∼9. In order to reduce the impact of cable capacitance, the amplifier is located adjacent to the Si sample, at the mixing chamber stage of a dilution refrigerator. For a current gain of ∼2.7×103, the power dissipation of the amplifier is 13 μW, the bandwidth is ∼1.3 MHz, and for frequencies above 300 kHz the current noise referred to input is ≤70 fA/Hz. With this amplification scheme, we are able to observe coherent oscillations of a P donor electron spin in isotopically enriched 28Si with 96% visibility.
In recent years, quantum computers have emerged as a disruptive technology capable of solving problems currently intractable for classical systems. Computation is performed using qubits, which exploit quantum properties like superposition and entanglement, and requires them to operate at cryogenic temperatures. As a result, quantum computers are built around cryostats that reach temperatures as low as \qty{10}{\milli\kelvin}. However, to deliver a significant advantage over conventional approaches, quantum computers must increase their qubit count, improve qubit quality, and adopt more sophisticated control and readout architectures. The integration of more complex or improved cryogenic electronics inside the cryostat can enhance the scalability of these systems, and is the topic of this thesis. The primary technology platform used in this work is based on cryogenic InGaAs/InP high-electron-mobility transistors (HEMTs). One objective was the development of cryogenic circuits that enhance the scalability of spin-qubit quantum computers by enabling efficient signal delivery in control and readout paths. To this end, cryogenic multiplexers were demonstrated with threshold voltages as low as \qty{90}{\milli\volt}, subthreshold swing of \qty{5}{\milli\volt\per dec}, and on-off ratio of 10710^7107 at \qty{4}{\kelvin}. In addition, a charge-storage array was developed for the local generation of qubit bias signals, using an operation scheme based on pulse trains to program voltage levels on capacitors that can be placed in proximity to qubit gates. A second objective was the fabrication of HEMTs with enhanced performance for use in cryogenic low-noise amplifiers, which are critical for qubit readout. Studies were performed to characterize self-heating, an effect that limits transistor performance at cryogenic temperatures. Moreover HEMTs with improved characteristics were fabricated, which achieved exceptional values in state-of-the-art metrics, including fT=f_T =fT​= \qty{622}{\giga\hertz}, fMAX=f_{MAX} =fMAX​= \qty{733}{\giga\hertz}, and a noise indication factor IDS/gm=\sqrt{I_{DS}} / g_m =IDS​​/gm​= \qty{0.17}{\sqrt{\volt \cdot \milli\meter / \siemens}} at \qty{4}{\kelvin}. These results represent a new record for the combination of high-frequency and low-noise performance in a cryogenic HEMT. These results establish the InGaAs/InP HEMT technology as a promising platform for the development of cryogenic circuits, and demonstrate its versatility in addressing multiple applications requiring both single-device performance and integration at the circuit level.
We examine a silicon-germanium heterojunction bipolar transistor (HBT) for cryogenic pre-amplification of a single electron transistor (SET). The SET current modulates the base current of the HBT directly. The HBT-SET circuit is immersed in liquid helium, and its frequency response from low frequency to several MHz is measured. The current gain and the noise spectrum with the HBT result in a signal-to-noise-ratio (SNR) that is a factor of 10–100 larger than without the HBT at lower frequencies. The transition frequency defined by SNR = 1 has been extended by as much as a factor of 10 compared to without the HBT amplification. The power dissipated by the HBT cryogenic pre-amplifier is approximately 5 nW to 5 μW for the investigated range of operation. The circuit is also operated in a single electron charge read-out configuration in the time-domain as a proof-of-principle demonstration of the amplification approach for single spin read-out.
Two versions of a cryogenic multistage pseudomorphic high-electron-mobility field-effect transistor amplifier (based on the AlGaAs/InGaAs/GaAs heterostructure) have been designed for quantum device readout and tested at an ambient temperature ∼380mK. The minimum noise temperature of the first amplifier version is below 110±25mK(∼80±20hf∕kB) at 28.6 MHz, estimated from the noise of input 10 kΩ resistance and coupled input tank circuit with an active resistance at the resonant frequency RS(f0)≈17.9kΩ. Its minimum voltage spectral noise density, with respect to the input, is about 200pV∕(Hz)1∕2 and the corner frequency of the 1∕f noise is close to 300 kHz. For the amplifier with the lowest designed back action, the minimum noise temperature below 130±30mK(∼100±25hf∕kB) at 26.8 MHz was estimated when coupled to an input tank circuit with RS(f0)≈61.8kΩ. The power consumption of the amplifiers is in the range of 100–600 μW.
We developed a high-speed and low-noise time-domain current measurement scheme using a homemade GaAs high-electron-mobility-transistor-based cryogenic transimpedance amplifier (TIA). The scheme is versatile for broad cryogenic current measurements, including semiconductor spin-qubit readout, owing to the TIA's having low input impedance comparable to that of commercial room-temperature TIAs. The TIA has a broad frequency bandwidth and a low noise floor, with a trade-off between them governed by the feedback resistance RFB. A lower RFB of 50 kΩ enables high-speed current measurement with a −3 dB cutoff frequency f−3dB = 28 MHz and noise-floor NF = 8.5 × 10−27 A2/Hz, while a larger RFB of 400 kΩ provides low-noise measurement with NF = 1.0 × 10−27 A2/Hz and f−3dB = 4.5 MHz. Time-domain measurement of a 2-nA peak-to-peak square wave, which mimics the output of the standard spin-qubit readout technique via charge sensing, demonstrates a signal-to-noise ratio (SNR) of 12.7, with the time resolution of 48 ns, for RFB = 200 kΩ, which compares favorably with the best-reported values for the radio frequency reflectometry technique. The time resolution can be further improved at the cost of the SNR (or vice versa) by using an even smaller (larger) RFB, with a further reduction in the noise figure possible by limiting the frequency band with a low-pass filter. Our scheme is best suited for readout electronics for cryogenic sensors that require a high time resolution and current sensitivity and, thus, provides a solution for various fundamental research and industrial applications.
Abstract The image-charge detection provides a new direct method for the detection of the Rydberg transition of electrons trapped on the surface of liquid helium. The interest in this method is motivated by the possibility to accomplish the spin state readout for a single trapped electron, thus opening a new pathway towards using electron spins on liquid helium for quantum computing. Here, we report on the image-charge detection of the Rydberg transition in a many-electron system confined in an array of 20 μ m wide and 4 μ m deep channels filled with superfluid helium. Such detection is made possible because of a significant enhancement of the image-charge signal due to close proximity of trapped electrons to the electrodes embedded in the microchannel structure. The transition frequency of electrons in the range of 400–500 GHz is highly controllable by the dc bias voltages applied to the device and is in a good agreement with our calculations. This work demonstrates that microchannel structures provide a suitable platform for electron manipulation and their quantum state detection, with a feasibility of scaling the detection method to a single electron.