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arXiv:2209.13060 · Nature Electronics

Multiplexed superconducting qubit control at millikelvin temperatures with a low-power cryo-CMOS multiplexer

R. Acharya, S. Brebels, Alexander Grill, Jeroen Verjauw, Ts. Ivanov, Daniel Pérez Lozano, Danny Wan, Jacques Van Damme, A. M. Vadiraj, Massimo Mongillo, B. Govoreanu, Jan Craninckx, Iuliana P. Radu, Kristiaan De Greve, Georges E. Gielen, Francky Catthoor, Anton Potočnik

Published Sep 25, 2023• 56 citations
arXivHTMLPDF

Abstract

Abstract Large-scale superconducting quantum computing systems entail high-fidelity control and readout of large numbers of qubits at millikelvin temperatures, resulting in a massive input-output bottleneck. Cryo-electronics, based on complementary metal-oxide-semiconductor (CMOS) technology, may offer a scalable and versatile solution to overcome this bottleneck. However, detrimental effects due to cross-coupling between the electronic and thermal noise generated during cryo-electronics operation and the qubits need to be avoided. Here we present an ultra-low power radio-frequency (RF) multiplexing cryo-electronics solution operating below 15 mK that allows for control and interfacing of superconducting qubits with minimal cross-coupling. We benchmark its performance by interfacing it with a superconducting qubit and observe that the qubit’s relaxation times (T1) are unaffected, while the coherence times (T2) are only minimally affected in both static and dynamic operation. Using the multiplexer, single qubit gate fidelities above 99.9%, i.e., well above the threshold for surface-code based quantum error-correction, can be achieved with appropriate thermal filtering. In addition, we demonstrate the capability of time-division-multiplexed qubit control by dynamically windowing calibrated qubit control pulses. Our results show that cryo-CMOS multiplexers could be used to significantly reduce the wiring resources for large-scale qubit device characterization, large-scale quantum processor control and quantum error correction protocols.

DOI
10.1038/s41928-023-01033-8

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IEEE International Symposium on Smart Electronic Systems (iSES)•Dec 18, 2023•2 citations
Abstract Large-scale superconducting quantum computing systems entail high-fidelity control and readout of large numbers of qubits at millikelvin temperatures, resulting in a massive input-output bottleneck. Cryo-electronics, based on complementary metal-oxide-semiconductor (CMOS) technology, may offer a scalable and versatile solution to overcome this bottleneck. However, detrimental effects due to cross-coupling between the electronic and thermal noise generated during cryo-electronics operation and the qubits need to be avoided. Here we present an ultra-low power radio-frequency (RF) multiplexing cryo-electronics solution operating below 15 mK that allows for control and interfacing of superconducting qubits with minimal cross-coupling. We benchmark its performance by interfacing it with a superconducting qubit and observe that the qubit’s relaxation times (T1) are unaffected, while the coherence times (T2) are only minimally affected in both static and dynamic operation. Using the multiplexer, single qubit gate fidelities above 99.9%, i.e., well above the threshold for surface-code based quantum error-correction, can be achieved with appropriate thermal filtering. In addition, we demonstrate the capability of time-division-multiplexed qubit control by dynamically windowing calibrated qubit control pulses. Our results show that cryo-CMOS multiplexers could be used to significantly reduce the wiring resources for large-scale qubit device characterization, large-scale quantum processor control and quantum error correction protocols.
Large-scale cryogenic quantum systems are constrained by an input-output bottleneck between room-temperature electronics and millikelvin stages, particularly in superconducting qubit platforms. This bottleneck is most acute for output lines, where bulky and expensive microwave components limit scalability. A promising approach for scalable characterization and testing is to perform signal multiplexing directly at the qubit plane. We demonstrate a cryogenic CMOS (cryoCMOS) RF multiplexer operating at 10 millikelvin with record-low static power consumption of 200 pW. The device provides < 2 dB insertion loss and > 30 dB isolation across DC-8 GHz. Direct connection to transmon qubits marginally affects coherence times in the range of 100 microseconds, enabling multiplexing of readout, flux and, in principle, XY drive lines. This work introduces cryoCMOS multiplexers as valuable tools for scalable, high-throughput cryogenic characterization and testing, and advances co-integrated quantum-classical control for future large-scale quantum processors.
Abstract Realizing a practically useful superconducting quantum computer will require a dramatic scale-up of quantum control electronics to meet the growth in required qubit counts. Conventional rack-based room-temperature control electronics impose severe constraints on wiring density, cost, and system footprint, creating a barrier to large-scale and fault-tolerant quantum computing. Here we demonstrate a hybrid quantum control architecture that combines cryogenic complementary metal-oxide semiconductor (cryo‑CMOS) application-specific integrated circuits (ASICs) for two‑qubit flux control with room‑temperature radio‑frequency electronics for single‑qubit control and readout. The resulting system achieves high density and scalable quantum control without compromising two‑qubit gate fidelity. Deployed on a 156‑qubit quantum processor, the cryo-CMOS subsystem achieves two‑qubit gate errors at the {10}^{-3} level, with a best randomized benchmarking error per gate of 8.4\times{10}^{-4}, stable operation over multi‑day timescales, and no measurable performance degradation as we increase the temperature of the cryo-CMOS ASICs from 7 to 20 K. Thermal analysis identifies cryo-CMOS chip operation near 20 K as a favorable regime, enabling efficient cooling of a large number of channels per cryostat. Compared against rack‑based flux-control, the cryo-CMOS subsystem achieves statistically indistinguishable two-qubit gate fidelities under matched gate settings and enables a tenfold improvement in system spatial footprint. These results establish cryo‑CMOS flux control as a practical and scalable foundation for large‑scale and fault-tolerant superconducting quantum systems.
Abstract The most promising quantum algorithms require quantum processors that host millions of quantum bits when targeting practical applications1. A key challenge towards large-scale quantum computation is the interconnect complexity. In current solid-state qubit implementations, an important interconnect bottleneck appears between the quantum chip in a dilution refrigerator and the room-temperature electronics. Advanced lithography supports the fabrication of both control electronics and qubits in silicon using technology compatible with complementary metal oxide semiconductors (CMOS)2. When the electronics are designed to operate at cryogenic temperatures, they can ultimately be integrated with the qubits on the same die or package, overcoming the ‘wiring bottleneck’3–6. Here we report a cryogenic CMOS control chip operating at 3 kelvin, which outputs tailored microwave bursts to drive silicon quantum bits cooled to 20 millikelvin. We first benchmark the control chip and find an electrical performance consistent with qubit operations of 99.99 per cent fidelity, assuming ideal qubits. Next, we use it to coherently control actual qubits encoded in the spin of single electrons confined in silicon quantum dots7–9 and find that the cryogenic control chip achieves the same fidelity as commercial instruments at room temperature. Furthermore, we demonstrate the capabilities of the control chip by programming a number of benchmarking protocols, as well as the Deutsch–Josza algorithm10, on a two-qubit quantum processor. These results open up the way towards a fully integrated, scalable silicon-based quantum computer.
Quantum computing promises an exponentially higher computational power than classical computers; although all the building blocks have become available, certain constraints still prevent quantum advantage. The fundamental challenge in building a practical quantum computer is integrating thousands of highly coherent qubits with the control and readout electronics. The need for a high‐coherence qubit drives the effort for quantum error correction algorithms to create fault‐tolerant quantum systems. Error correction becomes tangible in a quantum processor only in large numbers of qubits. Thus, the other challenge is reducing the number of physical interconnects (coaxial lines) between the quantum–classical interface and bulky room‐temperature electronics. To interface thousands of qubits, interconnects can be reduced by bringing the control and readout electronics near the quantum processor. Cryogenic complementary metal–oxide–semiconductor (CMOS) technology has been an ideal candidate for this purpose. Integrated control and readout at cryogenic temperatures require low power dissipation circuit designs and techniques such as frequency‐division multiplexing (FDM) due to the finite cooling power of a dilution refrigerator. Herein, an overview of each building block in a superconducting quantum computer is provided, focusing on scalability. Furthermore, this article is concluded with an outlook discussing current challenges and future directions for the scalable superconducting control and readout.
Abstract Quantum computers based on solid state qubits have been a subject of rapid development in recent years. In current noisy intermediate-scale quantum technology, each quantum device is controlled and characterised through a dedicated signal line between room temperature and base temperature of a dilution refrigerator. This approach is not scalable and is currently limiting the development of large-scale quantum system integration and quantum device characterisation. Here we demonstrate a custom designed cryo-CMOS multiplexer operating at 32 mK. The multiplexer exhibits excellent microwave properties up to 10 GHz at room and millikelvin temperatures. We have increased the characterisation throughput with the multiplexer by measuring four high-quality factor superconducting resonators using a single input and output line in a dilution refrigerator. Our work lays the foundation for large-scale microwave quantum device characterisation and has the perspective to address the wiring problem of future large-scale quantum computers.
A fault tolerant scalable quantum computer requires more than 1000 Qubits to perform real time state correction and to improve the Qubit coherence time. The dense wiring connections required between the quantum processor placed at a 100 mK temperature and the room temperature control and readout electronics serve as a limiting factor in this system. Qubit control and readout electronics operating at 4 K temperature, placed closer to a quantum processor inside the dilution refrigerator avoids the dense wiring connections to room temperature electronics, and hence, serve as a potential solution to realize a scalable quantum computer. However, with no CMOS process technology models available at cryogenic temperatures, the design of a fully integrated, ultra-low power Qubit control and readout electronics at a sub-1 mW power consumption proves to be extremely challenging. In recent years, there has been a huge rise in interest among the research communities to understand and solve the device and circuit level challenges at deep cryogenic temperatures. This paper presents an overview of the recently published active and passive device nonidealities, circuit design challenges and solutions, and the future research directions in the Qubit control and readout electronics operating at deep cryogenic temperatures.