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arXiv:2211.06667

Superconductor modulation circuits for Qubit control at microwave frequencies

Sasan Razmkhah, Ali Bozbey, Pascal Febvre

Published Nov 12, 2022• 3 citations
arXivHTMLPDF

Abstract

Readout and control of qubits are limiting factors in scaling quantum computers. An ideal solution is to integrate energy-efficient cryogenic circuits close to the qubits to perform control and pre-processing tasks. With orders of magnitude lower power consumption and hence lower noise, Single Flux Quantum (SFQ) and Adiabatic Quantum Flux Parametron (AQFP) superconductor logic families can reach ultimate performance at cryogenic temperatures. We have created a superconductor-based on-chip function generator to control qubits. The generated signal is modulated up to tens of GHz based on the external input waveform applied to the superconductor mixer stage. This circuit works at 4.2K. A radiofrequency (RF) matching circuit transmits the signal to the ~mK stage after digital amplification and noise reduction.

DOI
10.48550/arxiv.2211.06667

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Readout and control of qubits are limiting factors in scaling quantum computers. An ideal solution is to integrate energy-efficient cryogenic circuits close to the qubits to perform control and pre-processing tasks. With orders of magnitude lower power consumption and hence lower noise, Single Flux Quantum (SFQ) and Adiabatic Quantum Flux Parametron (AQFP) superconductor logic families can reach ultimate performance at cryogenic temperatures. We have created a superconductor-based on-chip function generator to control qubits. The generated signal is modulated up to tens of GHz based on the external input waveform applied to the superconductor mixer stage. This circuit works at 4.2K. A radiofrequency (RF) matching circuit transmits the signal to the ~mK stage after digital amplification and noise reduction.
Abstract Cryogenic qubit controllers (QCs) are the key to build large-scale superconducting quantum processors. However, developing scalable QCs is challenging because the cooling power of a dilution refrigerator is too small (~10 μW at ~10 mK) to operate conventional logic families, such as complementary metal-oxide-semiconductor logic and superconducting single-flux-quantum logic, near qubits. Here we report on a scalable QC using an ultra-low-power superconductor logic family, namely adiabatic quantum-flux-parametron (AQFP) logic. The AQFP-based QC, referred to as the AQFP-multiplexed QC (AQFP-mux QC), produces multi-tone microwave signals for qubit control with an extremely small power dissipation of 81.8 pW per qubit. Furthermore, the AQFP-mux QC adopts microwave multiplexing to reduce the number of coaxial cables for operating the entire system. As a proof of concept, we demonstrate an AQFP-mux QC chip that produces microwave signals at two output ports through microwave multiplexing and demultiplexing. Experimental results show an output power of approximately −80 dBm and on/off ratio of ~40 dB at each output port. Basic mixing operation is also demonstrated by observing sideband signals.
Quantum technologies are today regarded as one of the key technologies with huge implications to technological, economic and social developments in the next decades. Among the different platforms, superconducting implementations represent one of the most promising and are therefore pursued by several research institutions but also by numerous high-tech companies. Current research focusses e.g. on scaling towards a large number of qubits needed for practical implementations of this technology. Amongst the various realizations, adiabatic quantum flux parametron (AQFP) circuits have shown lowest power dissipation reaching Landauer limit. The operation of AQFP circuits down to mK temperature has been recently demonstrated. We will present a new concept for a digital control circuit based on the microwave pulse patters generated by single flux quantum circuits operating at mK temperatures. We discuss the circuit operation and the integration together with superconducting qubits to a compact and scalable approach for multi-Qubit control by digital pulse patterns.
Abstract The use of high-frequency input signals from room-temperature microwave sources makes it difficult to scale up the number of quantum bits in universal quantum computers. To address this issue, superconducting single flux quantum (SFQ) integrated circuits are being explored as suitable candidates for qubit manipulation in universal quantum computers. This paper deals with a scalable SFQ qubit control circuit (SQCC) structure that requires only low-frequency input. The circuit mainly consists of a pulse generator and a counter, that output the SFQ pulse train with adjustable frequency and a controllable number of pulses, which is applicable to control single-qubit Clifford operations. The design of low-voltage rapid single flux quantum (LV-RSFQ) and energy-efficient rapid single flux quantum (ERSFQ) for the SQCC achieves low power consumption and provides a basis for scaling up SQCC to control more qubits. The proposed circuits are fabricated under the SIMIT-Nb03 process and successfully pass test verification. The achieved test results reveal that the adjustable output frequency ranges of the SQCC based on the LV-RSFQ and ERSFQ designs in order are [2.40, 8.11] GHz and [4.81, 5.14] GHz. In the operating frequency range, the circuit is able to generate the correct number of SFQ pulses under control. The controllable number range is from 1 to 128. When the circuits operate at 5 GHz, the total power consumptions of the above circuits in order are 23.88 μW and 6.2 μW. All input signals are low-frequency signals, which frees the control of large-scale qubits from limitations caused by high-frequency inputs produced by room-temperature microwave sources.
An on-chip superconducting microwave pulse generator (MPG), incorporating rapid single-flux-quantum (RSFQ) logic gates and passive radio frequency (RF) components, is an energy-efficient solution for controlling superconducting quantum bits (qubits). Traditional RSFQ MPG designs, however, suffer from a large footprint as multiple RF components (including impedance matching networks, filters, etc.) are separately implemented one after another. In this Letter, we propose a compact on-chip MPG by introducing an integrated RF module. Using a generalized filter synthesis technique, the integrated RF module combines the functionalities of impedance matching and bandpass filtering as a single inductor-capacitor (LC) lumped network. Plenty of circuit elements can, thus, be saved, and the resultant LC network is applicable to both real and complex terminal impedance cases. For validation, a superconducting MPG adopting a fourth-order, 5 GHz centered, 100 MHz bandwidth integrated RF module is designed and fabricated, whose correct operations are confirmed through both simulation and measurement. These results raise the availability of controlling large-scale quantum systems by low-power superconductor technology in the future.
Current superconducting quantum computers (QC) rely on a brute-force scaling approach where quantum chips operating at the millikelvin stage inside dilution refrigerators are connected to room-temperature electronics via an ever-increasing number of signal wires. In order to drastically scale up such systems without facing refrigeration challenges, these quantum interface electronics need to be integrated at cryogenic temperatures, ideally at the same stage as qubits. In this paper, we show that, by employing energy-efficient digital superconducting microchips based on single flux quantum (SFQ) technology, all essential functions to operate a full stack quantum computer can be integrated at 10 mK. They include digital qubit charge control and magnetic flux control for single- and two-qubit gates, as well as digital qubit readout.