A Sub-GHz Impedance-Engineered Parametric Amplifier for the Readout of Sensors and Quantum Dots

Spins in silicon quantum devices are promising candidates for large-scale quantum computing. Gate-based sensing of spin qubits offers a compact and scalable readout with high fidelity, however, further improvements in sensitivity are required to meet the fidelity thresholds and measurement timescales needed for the implementation of fast feedback in error correction protocols. Here, we combine radio-frequency gate-based sensing at 622MHz with a Josephson parametric amplifier, that operates in the 500-800MHz band, to reduce the integration time required to read the state of a silicon double quantum dot formed in a nanowire transistor. Based on our achieved signal-to-noise ratio, we estimate that singlet-triplet single-shot readout with an average fidelity of 99.7% could be performed in 1 μs, well below the requirements for fault-tolerant readout and 30 times faster than without the Josephson parametric amplifier. Additionally, the Josephson parametric amplifier allows operation at a lower radio-frequency power while maintaining identical signal-to-noise ratio. We determine a noise temperature of 200mK with a contribution from the Josephson parametric amplifier (25%), cryogenic amplifier (25%) and the resonator (50%), showing routes to further increase the readout speed.

This study presents a comprehensive design approach focusing on quantum chip signal amplification by Josephson parametric amplifiers, and an integrated receiver for detecting ultra-low-level quantum signals. Quantum theory is used to analyze the dynamics of a transmon qubit coupled to a transmission line, entanglement between them, and design a parametric amplifier to amplify the quantum signals. Integration of these quantum devices with a 45 nm CMOS system-on-chip receiver creates a sophisticated blend of quantum and classical elements. The transmon qubit and parametric amplifier as a quantum chip, operating at 10 mK, are evaluated for key quantum metrics such as entanglement, Stoke projector probabilities, and parametric amplifier gain. Simultaneously, the resulting receiver combines high-performance components, including a low-noise amplifier with 0.76 dB noise figure in a broad bandwidth, a sweepable 5.0 GHz sinusoidal wave generator, and a purpose-designed mixer for C-band to zero-intermediate frequency (IF) conversion. An intermediate frequency amplifier with flat 26 dB gain and its low-pass filter property generates a pure sinusoidal wave at zero-IF, suitable for subsequent processing at room temperature. This design achieves a notable balance with low power consumption (∼122 mW), a noise figure less than 0.9 dB, high gain (∼65 dB), a wide bandwidth of 3.6 GHz, and compact dimensions (0.6 × 0.4 mm2). The fully integrated receiver, capable of reading out at least 90 qubits, positions this design for potential applications in quantum computing. Post-simulation validations at room temperature underscore the promising and innovative nature of this approach.

Superconducting parametric amplifiers offer the capability to amplify feeble signals with extremely low levels of added noise, potentially reaching quantum-limited amplification. This characteristic makes them essential components in the realm of high-fidelity quantum computing and serves to propel advancements in the field of quantum sensing. In particular, Traveling-Wave Parametric Amplifiers (TWPAs) may be especially suitable for practical applications due to their multi-Gigahertz amplification bandwidth, a feature lacking in Josephson Parametric Amplifiers (JPAs), despite the latter being a more established technology. This paper presents recent developments of the DARTWARS (Detector Array Readout with Traveling Wave AmplifieRS) project, focusing on the latest prototypes of Kinetic Inductance TWPAs (KITWPAs). The project aims to develop a KITWPA capable of achieving 20 dB of amplification. To enhance the production yield, the first prototypes were fabricated with half the length and expected gain of the final device. In this paper, we present the results of the characterization of one of the half-length prototypes. The measurements revealed an average amplification of approximately 9 dB across a 2 GHz bandwidth for a KITWPA spanning 17 mm in length.

Quantum computing systems and fundamental physics experiments using superconducting technologies frequently require signal amplification chains operating near the quantum limit of added noise. Both Josephson parametric amplifiers (JPAs) and traveling wave parametric amplifiers (TWPAs) have been used as first-stage amplifiers to enable readout chains operating within a few quanta or less of the quantum limit. These devices are also presently entering the commercial industry. However, nearly all demonstrations and existing products require bulky external microwave components for interconnection and application of requisite biases. These components – cabling interconnects, bias tees, directional couplers, and diplexers – increase the overall amplifier footprint, installation complexity, and reduce already limited available cryogenic volumes. Additionally, these components introduce loss and reflections which impact the measurement efficiency and readout system noise performance; thus making it more difficult to operate near the quantum limit. Here we present the design and validation of microfabricated bias tees and directional couplers for operating three-wave mixing kinetic inductance TWPAs (KITs). We report the performance of KITs integrated with the microfabricated rf components. Using these devices we demonstrate reduction in the amplifier installation footprint by a factor of nearly five and elimination of all external, lossy microwave components previously required to operate a KIT. Our device displays a 2.8 GHz 3 dB bandwidth with a median true gain of 17.5 dB and median system noise of 3.4 quanta. These efforts represent the first full integration of all rf components mandatory for TWPA operation on-chip. Our results mark significant progress towards the miniaturization and simplification of parametric amplifier setups and will aid in their more widespread applicability.

Quantum two-mode squeezed (QTMS) radar, inspired by quantum illumination but without joint measurements in the receiver, has shown promise in target detection. However, the current prototype of quantum radar, using full-microwave superconducting components, faces challenges in achieving long-range performance. In this study, we propose the integration of an array of Josephson parametric amplifiers (JPAs) in a dilution refrigerator to enhance the performance of QTMS quantum radar. Through the evaluation of signal-to-noise ratio (SNR) and receiver operating characteristic (ROC) metrics, we demonstrate the effectiveness of this enhancing strategy. Our results indicate that the presence of an array of two JPAs significantly improves both the SNR and the detection probability compared to a single JPA configuration, thereby boosting the overall performance of QTMS radar. The key factor of this improvement is the cross-correlation between JPAs, which has a notable impact on the analytical outcomes of the quantum radar. This research provides valuable insights to engineers who want to optimize the design of advanced quantum QTMS radar systems.

Bolometers are radiation sensors that are central to wide areas such as dark matter search, radio astronomy, material science, and qubit readouts, among others. There have been different kinds of bolometer realizations in the recent past. The challenge is to have a single device that combines high sensitivity, broad bandwidth, and a fast readout scheme. Here we demonstrate the usage of Josephson parametric amplifiers (JPA) as highly sensitive bolometers. Our key finding is that the Kerr non-linearity of the JPA boosts the device's sensitivity. When the bolometer is biased in the non-linear regime, it enhances the up-converted signals (~100 times), resulting in an order of magnitude improvement in sensitivity compared to the linear regime. In the non-linear biasing, we achieve a NEP~500 aW/ . Our device offers a fast detection scheme with a thermal time constant of 4.26 μs and an intrinsic JPA time constant of 70 ns. Our work integrates a JPA into a bolometer, enabling a fast and sensitive operation compared to previously studied graphene-based bolometers. Our study demonstrates a way forward to improve the quantum sensors based on 2D materials by leveraging the inherent non-linear response.

Harmonic oscillators might be one of the most fundamental entities described by physics. Yet they stay relevant in recent research. The topological properties associated with exceptional points that can occur when two modes interact have generated much interest in recent years. Harmonic oscillators are also at the heart of new quantum technological applications: the long lifetime of high-Q resonators make them advantageous as quantum memories, and they are employed for narrowband processing of quantum signals, as in Josephson parametric amplifiers. The goal of this thesis is to explore different fundamental regimes of two coupled harmonic oscillators using cavity optomechanics as the experimen- tal platform. With consistent progress in attaining ever increasing Q factors, mechanical and electromagnetic resonators realize near-ideal harmonic oscillators. By parametrically modulating the nonlinear optomechanical interaction between them, an effective linear coupling is achieved, which is tunable in strength and in the relative frequencies of the two modes. Thus cavity optomechanics provides a framework with excellent control over system parameters for the study of two coupled harmonic modes. The specific optomechanical implementation employed are superconducting circuits with the vibrating top plate of a capacitor as the mechanical element. Multimode optomechanical circuits are realized, with two microwave modes interacting with one or two mechanical oscillators. The supplementary modes serve either as intermediaries in the relation of the two modes of interest, or as auxiliaries used to control a parameter of the system. Three main experimental results are achieved. First, an auxiliary microwave mode allows the engineering of the effective dissipation rate of a mechanical oscillator. The latter then acts as a reservoir for the main microwave mode with which it interacts. The microwave mode susceptibility can be tuned, resulting in an instability akin to that of a maser and in resonant amplification of incoming microwave signals with an added noise close to the quantum minimum. Second, we study the conditions for a nonreciprocal interaction between two microwave modes, when the information flows in one direction but not in the other. The two modes interact through two mechanical oscillators, leading to frequency conversion between the two cavities. Dissipation in the mechanical modes is essential to the scheme in two ways: it provides a reciprocal phase necessary for the interference and eliminates the unwanted signals. Third, level attraction between a microwave and a mechanical mode is demonstrated, where the eigenfrequencies of the system are drawn closer as the result of interaction, rather distancing themselves as in the more usual case of level repulsion. The phenomenon is theoretically connected to exceptional points, and a general classification of the possible regimes of interaction between two harmonic modes is exposed, including level repulsion and attraction as special cases.

We discuss the feasibility of using microwave quantum radars in biomedical sensing applications, with a heavy focus on the equipment needed to operate such radars. A recent microwave quantum radar experiment used a device called a Josephson parametric amplifier (JPA) to generate quantum entangled signals. Since JPAs or JPA-like devices are expected to be used in most quantum radar implementations in the foreseeable future, we examine the operating requirements of JPAs. We find that the most important requirement for operating a JPA is the need for cryogenic cooling. This is easily accommodated in medical environments such as hospitals, so it is natural to consider whether quantum radars could work for biomedical sensing. We then find that, in fact, many of the strengths of quantum radars are naturally suited to medical contexts. We therefore conclude that the case for using JPA-based quantum radars for medical sensing is a strong one.

Josephson junctions (JJs) and their tunable properties, including their nonlinearities, play an important role in superconducting qubits and amplifiers. JJs together with the circuit quantum electrodynamics architecture form many key components of quantum information processing1. In quantum circuits, low-noise amplification of feeble microwave signals is essential, and Josephson parametric amplifiers (JPAs)2 are the widely used devices. The existing JPAs are based on Al-AlOx-Al tunnel junctions realized in a superconducting quantum interference device geometry, where magnetic flux is the knob for tuning the frequency. Recent experimental realizations of two-dimensional (2D) van der Waals JJs3-5 provide an opportunity to implement various circuit quantum electrodynamics devices6-8 with the added advantage of tuning the junction properties and the operating point using a gate potential. While other components of a possible 2D van der Waals circuit quantum electrodynamics architecture have been demonstrated, a quantum-noise-limited amplifier, an essential component, has not been realized, to the best of our knowledge. Here we implement a quantum-noise-limited JPA using a graphene JJ, that has a linear resonance gate tunability of 3.5 GHz. We report 24 dB amplification with 10 MHz bandwidth and -130 dBm saturation power, a performance on par with the best single-junction JPAs2,9. Importantly, our gate-tunable JPA works in the quantum-limited noise regime, which makes it an attractive option for highly sensitive signal processing. Our work has implications for novel bolometers; the low heat capacity of graphene together with JJ nonlinearity can result in an extremely sensitive microwave bolometer embedded inside a quantum-noise-limited amplifier. In general, this work will open up the exploration of scalable device architectures of 2D van der Waals materials by integrating a sensor with the quantum amplifier.

We report on the use of a CMOS Contrast-based Binary Vision Sensor (CBVS), with embedded contrast extraction, for gesture detection applications. The first advantage of using this sensor over commercial imagers is a dynamic range of 120dB, made possible by a pixel design that effectively performs auto-exposure control. Another benefit is that, by only delivering the pixels detecting a contrast, the sensor requires a very limited bandwidth. We leverage the sensor's fast 150µs readout speed, to perform multiple reads during a single exposure; this allows us to estimate gray-level information from the otherwise binary pixels. As a use case for this novel readout strategy, we selected in-car gesture detection, for which we carried out preliminary tests showing encouraging results.

Hybrid photon counting (HPC) detectors are widely used at both synchrotron facilities and in-house laboratories. The features of HPC detectors, such as no readout noise, high dynamic range, high frame rate, excellent point spread function, no blurring etc. along with fast data acquisition, provide a high-performance detector with a low detection limit and high sensitivity. Several HPC detector systems have been developed around the world. A number of them are commercially available and used in academia and industry. One of theimportant features of an HPC detector is a fast readout speed. Most HPC detectors can easily achieve over 1000 frames s-1, one or two orders of magnitude faster than conventional CCD detectors. Nevertheless, advanced scientific challenges require ever faster detectors in order to study dynamical phenomena in matter. The XSPA-500k detector can achieve 56 kframes s-1 continuously, without dead-time between frames. Using `burst mode', a special mode of the UFXC32k ASIC, the frame rate reaches 1 000 000 frames s-1. XSPA-500k was fully evaluated at the Metrology beamline at Synchrotron SOLEIL (France) and its readout speed was confirmed by tracking the synchrotron bunch time structure. The uniformity of response, modulation transfer function, linearity, energy resolution and other performance metrics were also verified either with fluorescence X-rays illuminating the full area of the detector or with the direct beam.

In the two microwave (MW) cross-shaped cavity magnon system, we describe a method to produce multipartite entanglement and quantum steering. To achieve squeezed states of the magnons, a Josephson parametric amplifier (JPA) creates a squeezed vacuum field that drives the two cavities. We theoretically demonstrate that the cavity-cavity entanglement can be generated at the resonance point, however, increasing the cavity and magnon decay rates generate the cavity-magnon entanglement. By changing the squeezing parameter and increasing the decay rates, we can transfer the cavity-cavity entanglement to cavity-magnon entanglement. Furthermore, the cavity-cavity entanglement (survive up to 2.8 K) was not only found to be much stronger but also more robust as compared to cavity-magnon entanglement (survive up to 0.4 K). More importantly, the genuine photon-magnon-photon tripartite entanglement could be achieved, which is robust against thermal fluctuations and depends strongly on the squeezing parameter. Furthermore, for the current dual cavity-magnon system, two-way quantum steering is found when the optomagnonical couplings are equal. The current study offers a straightforward and practical method for achieving multipartite quantum correlations.

Josephson parametric amplifiers (JPA) are promising devices for applications in circuit quantum electrodynamics and for studies on propagating quantum microwaves because of their good noise performance. In this work, we present a systematic characterization of a flux-driven JPA at millikelvin temperatures. In particular, we study in detail its squeezing properties by two different detection techniques. With the homodyne setup, we observe the squeezing of vacuum fluctuations by superposing signal and idler bands. For a quantitative analysis, we apply dual-path cross-correlation techniques to reconstruct the Wigner functions of various squeezed vacuum and thermal states. At 10 dB signal gain, we find 4.9 ± 0.2 dB squeezing below the vacuum. In addition, we discuss the physics behind squeezed coherent microwave fields. Finally, we analyze the JPA noise temperature in the degenerate mode and find a value smaller than the standard quantum limit for phase-insensitive amplifiers.

A Monolithic Active Pixel Sensor prototype for the CEPC vertex detector

Spins in semiconductor quantum dots hold great promise as building blocks of quantum processors. Trapping them in Si MOS transistorlike devices eases future industrial-scale fabrication. Among the potentially scalable readout solutions, gate-based dispersive radio-frequency reflectometry only requires the already existing transistor gates to read a quantum dot state, which alleviates the need for additional elements. In this effort toward scalability, traveling-wave superconducting parametric amplifiers significantly enhance the readout signal-to-noise ratio (SNR) by reducing the noise below that of typical cryogenic low-noise amplifiers, while offering a broad amplification band, essential to multiplex the readout of multiple resonators. In this work, we demonstrate a 3-GHz gate-based reflectometry readout of electron charge states trapped in quantum dots formed in Si MOS multigate devices, with SNR enhanced due to a Josephson traveling-wave parametric amplifier (JTWPA). The broad tunable 2-GHz amplification bandwidth combined with more than 10-dB ON-OFF SNR improvement of the JTWPA enables frequency and time-division-multiplexed readout of interdot transitions, and noise performance consistent with JTWPA characteristics at higher frequencies. In addition, owing to a design without superconducting loops and with a metallic ground plane, the JTWPA is flux insensitive and shows stable performance up to a magnetic field of 1.1 T at the quantum dot device, compatible with standard Si MOS spin-qubit experiments.