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Modern Instrumentation

Low-Noise Amplification, Detection and Spectroscopy of Ultra-Cold Systems in RF Cavities

M. H. S. Bukhari, Zahoor H. Shah

Published Jan 1, 2016• 4 citations
Publisher

Abstract

The design and development of a cryogenic Ultra-Low-Noise Signal Amplification (ULNA) and detection system for spectroscopy of ultra-cold systems are reported here for the operation in the 0.5 - 4 GHz spectrum of frequencies (the “L” and “S” microwave bands). The design is suitable for weak RF signal detection and spectroscopy from ultra-cold systems confined in cryogenic RF cavities, as entailed in a number of physics, physical chemistry and analytical chemistry applications, such as NMR/NQR/EPR and microwave spectroscopy, Paul traps, Bose-Einstein Condensates (BEC’s) and cavity Quantum Electrodynamics (cQED). Using a generic Low-Noise Amplifier (LNA) architecture for a GaAs enhancement mode High-Electron Mobility FET device, our design has especially been devised for scientific applications where ultra-low-noise amplification systems are sought to amplify and detect weak RF signals under various conditions and environments, including cryogenic temperatures, with the least possible noise susceptibility. The amplifier offers a 16 dB gain and a 0.8 dB noise figure at 2.5 GHz, while operating at room temperature, which can improve significantly at low temperatures. Both dc and RF outputs are provided by the amplifier to integrate it in a closed-loop or continuous-wave spectroscopy system or connect it to a variety of instruments, a factor which is lacking in commercial LNA devices. Following the amplification stage, the RF signal detection is carried out with the help of a post-amplifier and detection system based upon a set of Zero-Bias Schottky Barrier Diodes (ZBD’s) and a high-precision ultra-low noise jFET operational amplifier. The scheme offers unique benefits of sensitive detection and very-low noise amplification for measuring extremely weak on-resonance signals with substantial low- noise response and excellent stability while eliminating complicated and expensive heterodyne schemes. The LNA stage is fully capable to be a part of low-temperature experiments while being operated in cryogenic conditions down to about 500 mK.

DOI
10.4236/mi.2016.52002

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The design and development of a cryogenic Ultra-Low-Noise Signal Amplification (ULNA) and detection system for spectroscopy of ultra-cold systems are reported here for the operation in the 0.5 - 4 GHz spectrum of frequencies (the “L” and “S” microwave bands). The design is suitable for weak RF signal detection and spectroscopy from ultra-cold systems confined in cryogenic RF cavities, as entailed in a number of physics, physical chemistry and analytical chemistry applications, such as NMR/NQR/EPR and microwave spectroscopy, Paul traps, Bose-Einstein Condensates (BEC’s) and cavity Quantum Electrodynamics (cQED). Using a generic Low-Noise Amplifier (LNA) architecture for a GaAs enhancement mode High-Electron Mobility FET device, our design has especially been devised for scientific applications where ultra-low-noise amplification systems are sought to amplify and detect weak RF signals under various conditions and environments, including cryogenic temperatures, with the least possible noise susceptibility. The amplifier offers a 16 dB gain and a 0.8 dB noise figure at 2.5 GHz, while operating at room temperature, which can improve significantly at low temperatures. Both dc and RF outputs are provided by the amplifier to integrate it in a closed-loop or continuous-wave spectroscopy system or connect it to a variety of instruments, a factor which is lacking in commercial LNA devices. Following the amplification stage, the RF signal detection is carried out with the help of a post-amplifier and detection system based upon a set of Zero-Bias Schottky Barrier Diodes (ZBD’s) and a high-precision ultra-low noise jFET operational amplifier. The scheme offers unique benefits of sensitive detection and very-low noise amplification for measuring extremely weak on-resonance signals with substantial low- noise response and excellent stability while eliminating complicated and expensive heterodyne schemes. The LNA stage is fully capable to be a part of low-temperature experiments while being operated in cryogenic conditions down to about 500 mK.
Large-scale superconducting quantum computers require massive numbers of high-performance cryogenic low-noise amplifiers (cryo-LNA) for qubit readout. Here we present a C-Band monolithic microwave integrated circuit (MMIC) cryo-LNA for this purpose. This cryo-LNA is based on 150 nm GaAs pseudomorphic high electron mobility transistor (pHEMT) process and implemented with a three-stage cascaded architecture, where the first stage adopts careful impedance match to optimize the noise and return loss. The integration of negative feedback loops adopted in the second and third-stage enhances the overall stability. Moreover, the pHEMT-self bias and current multiplexing circuitry structure facilitate the reduction of power consumption and require only single bias line. Operating at an ambient temperature of 3.6 K and consuming 15 mW, the cryo-LNA demonstrates good performance in the C-band, reaching a 5 K equivalent noise temperature and an average gain of 40 dB. We further benchmark this cryo-LNA with superconducting qubits, achieving an average single-shot dispersive readout fidelity of 98.3% without assistance from a quantum-limited parametric amplifier. The development of GaAs cryo-LNA diversifies technical support necessary for large-scale quantum applications.
The cryogenic indium phosphide (InP) high-electron-mobility transistor (HEMT) low-noise amplifier (LNA) is used for the readout amplification of qubits at444K where cooling capabilities are limited implying that the dc power of the active circuits is an essential design constraint. In this article, the RF and noise performance of the InP HEMT under ultralow-power (ULP) operation at444K has been characterized. The small-signal and noise parameter model of the InP HEMT was extracted down to 1μ\muμW. The tradeoff between noise performance and dc power consumption was analyzed in terms of the drain current and drain voltage. A 4–6 GHz hybrid cryogenic HEMT LNA designed for qubit readout and optimized for lowest noise below111mW dc power consumption was fabricated. The measured performance of the LNA at444K attained 23.1 dB average gain and 2.0 K average noise temperature at 200μ\muμW dc power.
A low-noise cryogenic amplifier for the measurement of weak microwave signals at sub-Kelvin temperatures is constructed. The amplifier has five stages based on SiGe bipolar heterostructure transistors and has a gain factor of 35 dB in the frequency band from 100 MHz to 4 GHz at an operating temperature of 800 mK. The parameters of a superconducting quantum bit measured with this amplifier in the ultralow-power mode are presented as an application example. The amplitude–frequency response of the “supercon-ducting qubit–coplanar cavity” structure is demonstrated. The ground state of the qubit is characterized in the quasi-dispersive measurement mode.
Large-scale superconducting quantum computers require massive numbers of high-performance cryogenic low-noise amplifiers (cryo-LNAs) for qubit readout. Here we presented a C-band monolithic microwave integrated circuit (MMIC) cryo-LNA for this purpose. This cryo-LNA is based on a 150 nm gallium arsenide (GaAs) pseudomorphic high electron mobility transistor (pHEMT) process and implemented with a three-stage cascaded architecture, where the first stage adopts careful impedance matching to optimize the noise and return loss. The integration of negative feedback loops adopted in the second and third stages enhances the overall stability. Moreover, the pHEMT self-bias and current multiplexing circuitry structure facilitate the reduction of power consumption and require only a single bias line. Operating at an ambient temperature of 3.6 K and consuming 15 mW, the cryo-LNA demonstrates good performance in the C-band, reaching a minimum noise temperature of 4 K and an average gain of 40 dB. We further benchmarked this cryo-LNA with superconducting qubits, achieving an average single-shot dispersive readout fidelity of 98.3% without assistance from a quantum-limited parametric amplifier. The development of GaAs cryo-LNA diversifies technical support necessary for large-scale quantum applications.
The design of a hi-Q resonant RF cavity with coupled detection scheme and associated instrumentation is reported for studying quantum vacuum within the framework of Quantum Electrodynamics (QED), the quantum theory of interaction of matter with radiation. Although this system could possibly serve in any general QED, cavity QED and RF applications in the range of a few GHz, the design was specifically devised for an experiment in studying intrinsic noise in quantum vacuum owing to vacuum fluctuations, which we call “Eavesdropping on Vacuum”. The center frequency of the cavity is 2.75GHz (which may be modified slightly to around 2.5GHz band for use in contemporary WiLAN and WiFi RF applications), with a high Q value. Initial design is made using copper but in the next stage it will be replaced with Niobium for use in low-temperature (around 0.1-0.3K) studies, making it an SRF (Superconducting Radio Frequency) cavity. A carefully devised scheme of sensitive RF detectors and ultra-low-noise cryogenic Low-Noise Amplifiers (cLNA) is an integral part of the cavity system. Detection element is an array of cavity-backed Au or Au-NbN spiral antennas in association with GaAs Schottky Barrier Diodes (SBD's), in conjunction with GaAs/InP HEMT's working in the GHz to THz regime. External fields are achieved with the help of time-dependent RF fields delivered to the cavity with the help of an antenna coupled with a GaAs Resonant Tunneling Diode (RTD). In addition to the cavity design, this report presents an overview of the detection scheme as well as necessary instrumentation, including RF detection, amplification, and the DAQ (Data Acquisition) required for digital read-out.
This work presents the design and optimization of a low-noise amplifier (LNA) for qubit readout in cryogenic environments of 3 − 4 K. The proposed LNA achieves wide bandwidth (4 GHz), high gain (47.0 dB), and sufficient linearity (IIP 3 = −34 dBm), while maintaining power consumption below 50 mW, making it suitable for integration into quantum computing systems. The amplifier is based on multi-stage cascode architectures with integrated inductances and impedance-matching techniques to optimize performance for a centre frequency of 5 GHz. While the results demonstrate good performance, there is still room for improvement in the S11parameter and the noise figure (NF ), which could benefit from a more refined transformer model. The proposed design represents a significant step toward integrating high-efficiency readout electronics into quantum computing architectures.