Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:1902.02911 · Physical Review Applied

Hardware-Efficient Qubit Control with Single-Flux-Quantum Pulse Sequences

Kangbo Li, R. McDermott, Maxim Vavilov

Published Jul 24, 2019• 55 citations
arXivHTMLPDF

Abstract

Single-flux-quantum (SFQ) digital logic is an attractive candidate for classical control and monitoring of large-scale quantum processors based on superconducting qubits. The authors describe a control approach based on repeated irradiation of the qubits with short registers of classical bits, which can be stored locally in compact SFQ registers and streamed to the quantum array at a high rate. Numerical simulations show achievable gate fidelity in excess of 99.99%; moreover, the approach allows control of many qubits resonating at different frequencies with a single, global SFQ clock. As a result, the scheme is well matched to the control of a scalable two-dimensional surface code.

DOI
10.1103/physrevapplied.12.014044

Related papers

Digital Coherent Control of a Superconducting Qubit

E. Leonard, M. A. Beck, J. Nelson +16 more

Superconducting qubits are conventionally controlled with shaped microwave pulses from a microwave carrier tone. This works well for small systems, but is difficult to scale up to the millions of qubits needed for a general-purpose quantum computer. Instead, the authors suggest irradiating a qubit with trains of quantized flux pulses derived from single flux quantum (SFQ) digital logic. The pulses are generated by an SFQ driver circuit cofabricated on the qubit chip. This work opens the door to tight integration of a quantum array with a classical coprocessor, to lower wiring heat load, latency, and overall system footprint.

arXiv:1806.07930•Physical Review Applied•Jan 7, 2019•141 citations

Digital Readout and Control of a Superconducting Qubit

Caleb Howington

In the quest to build a fault-tolerant quantum computer, superconducting circuits based on Josephson junctions have emerged as a leading architecture. Coherence times have increased significantly over the last two decades, and processors with ∼ 50 qubits have been experimentally demonstrated. These systems traditionally utilize microwave frequency control signals, and heterodyne based detection schemes for measurement. Both of these techniques rely heavily on room temperature microwave generators, high-bandwidth lines from room temperature to millikelvin temperatures, and bulky non-reciprocal elements such as cryogenic microwave isolators. Reliance on these elements makes it impractical to scale existing devices up a single order of magnitude, let alone the 5-6 orders of magnitude needed for performing fault-tolerant quantum algorithms. Here, I present results that suggesting superconducting digital logic, namely Single Flux Quantum (SFQ) logic, can replace analog control and measurement techniques, avoiding the significant overhead involved. I describe a scheme for measuring qubits with a device known as a Josephson Photomultiplier (JPM), which crucially stores the result of a qubit measurement in a classical circulating supercurrent within the device and allows for integration with SFQ detection circuitry. This technique is experimentally demonstrated, with single-shot measurement fidelity of 92%. Two methods for accessing this measurement result are presented, one utilizing ballistic fluxons, and another utilizing flux comparison. Initial experimental results of the latter are presented. In addition, I describe a scheme for controlling qubits with sequences of digital SFQ pulses. This method is then used to control a qubit without a microwave signal generator, with results of an average single-qubit gate fidelity of around 95%. When combined, these techniques form a nearly fully digital interface to superconducting qubits, which could allow these systems to scale much more easily.

•Jan 1, 2019•0 citations

Single-Flux-Quantum-Activated Controlled- Z Gate for Transmon Qubits

Yifeng Wang, Wei Gao, Kaihui Liu +3 more

Single-flux-quantum (SFQ) digital circuitry has great potential in building a scalable control system of superconducting qubits. In this work, we describe a practical SFQ-based two-qubit gate for transmon qubits. The controlled-$Z$ (CZ) gate is activated by near-resonant SFQ-pulse trains near the target transition involving the second excited state. Numerical simulations show that the fidelity of a SFQ-activated CZ gate in excess of 99.9% is achievable within 100-ns gate time. We evaluate the CZ gate error caused by leakage and SFQ-pulse width. Combined with the proposed feasible expansion methods, this work is a supplement to the scalable and integratable superconducting-qubit control system based on SFQ digital logic.

Physical Review Applied•Apr 11, 2023•10 citations

SFQ-Driven Pulse-Phase Sequence Generator for Superconducting Qubit Control

Meriam Gay Bautista, Patricia Gonzalez-Guerrero, Anastasiia Butko

The convergence of quantum computing and high-performance computing (HPC) necessitates innovative approaches to qubit control and coherence for scalable quantum systems. In this work, we explore the integration of superconducting Single-Flux Quantum (SFQ) digital circuits to enhance quantum state manipulation, leveraging their potential for high-speed, energy-efficient classical control. Our approach maps SFQ pulse trains and configurable SFQ-based switches to discrete phase shifts, enabling efficient qubit state transformations with minimal decoherence overhead. We introduce a classically driven SFQ-based quantum gate implementation, where SFQ pulses orchestrate the state evolution of qubits. To support dynamic and flexible qubit control within hybrid quantum-HPC architectures, we design and implement a multi-frequency SFQ pulse generator, capable of generating tailored pulse sequences that seamlessly interface with SQUID-based resonator-qubit cavities. This work demonstrates a promising path toward integrating quantum accelerators with classical HPC infrastructure, opti-mizing quantum-classical workflows, and enabling scalable, high-performance quantum computation.

IEEE International Symposium on Parallel & Distributed Processing, Workshops and Phd Forum•Jun 3, 2025•1 citation

Enabling Classical-Quantum Interface Using Digital SFQ for Pulse-Phase Driven Control for Superconducting Qubits

Meriam Gay Bautista, Patricia Gonzalez-Guerrero, George Michelogiannakis +1 more

In the interest of alleviating qubit coherence constraints and making quantum control circuits more efficient, this paper explores qubit control using superconducting Single-Flux Quantum (SFQ) digital circuits. By using SFQ pulse trains and SFQ switches, we represent qubit state transformations through their equivalent phase changes, where each SFQ pulse represents a phase change of certain degrees. We propose classical-based unitary quantum gates represented by SFQ pulses. We create a classical equivalent model for quantum gates based on an SFQ-based parametric pulse sequence equivalent to quantum Pauli gates. To generate pulse sequences of configurable parameters, we implement a versatile multi-frequency pulse generator that seamlessly integrates with the qubit-resonator cavity.

IEEE International Symposium on Circuits and Systems proceedings•May 25, 2025•0 citations

Compact pulse schedules for high-fidelity single-flux quantum qubit control

Ross Shillito, Florian Hopfmueller, Bohdan Kulchytskyy +1 more

In the traditional approach to controlling superconducting qubits using microwave pulses, the field of pulse shaping has emerged in order to assist in the removal of leakage and increase gate fidelity. However, the challenge of scaling microwave control electronics has created an opportunity to explore alternative methods such as single-flux quantum (SFQ) pulses. For qubits controlled by SFQ pulses, high fidelity gates can be achieved by optimizing the binary control sequence. We extend the notion of the derivative removal by adiabatic gate (DRAG) framework a transmon qubit controlled by SFQ drivers. The proposed implementation of SFQ pulse sequences can be stored in 22 bits or fewer, with gate fidelities exceeding 99.99%. This modest memory requirement could help reduce the footprint of the SFQ coprocessors and power dissipation while preserving their inherent advantages of scalability and cost-effectiveness.

arXiv:2309.04606•Physical Review Applied•May 13, 2025•4 citations
Single-flux-quantum (SFQ) digital logic is an attractive candidate for classical control and monitoring of large-scale quantum processors based on superconducting qubits. The authors describe a control approach based on repeated irradiation of the qubits with short registers of classical bits, which can be stored locally in compact SFQ registers and streamed to the quantum array at a high rate. Numerical simulations show achievable gate fidelity in excess of 99.99%; moreover, the approach allows control of many qubits resonating at different frequencies with a single, global SFQ clock. As a result, the scheme is well matched to the control of a scalable two-dimensional surface code.
Superconducting qubits are conventionally controlled with shaped microwave pulses from a microwave carrier tone. This works well for small systems, but is difficult to scale up to the millions of qubits needed for a general-purpose quantum computer. Instead, the authors suggest irradiating a qubit with trains of quantized flux pulses derived from single flux quantum (SFQ) digital logic. The pulses are generated by an SFQ driver circuit cofabricated on the qubit chip. This work opens the door to tight integration of a quantum array with a classical coprocessor, to lower wiring heat load, latency, and overall system footprint.
In the quest to build a fault-tolerant quantum computer, superconducting circuits based on Josephson junctions have emerged as a leading architecture. Coherence times have increased significantly over the last two decades, and processors with ∼ 50 qubits have been experimentally demonstrated. These systems traditionally utilize microwave frequency control signals, and heterodyne based detection schemes for measurement. Both of these techniques rely heavily on room temperature microwave generators, high-bandwidth lines from room temperature to millikelvin temperatures, and bulky non-reciprocal elements such as cryogenic microwave isolators. Reliance on these elements makes it impractical to scale existing devices up a single order of magnitude, let alone the 5-6 orders of magnitude needed for performing fault-tolerant quantum algorithms. Here, I present results that suggesting superconducting digital logic, namely Single Flux Quantum (SFQ) logic, can replace analog control and measurement techniques, avoiding the significant overhead involved. I describe a scheme for measuring qubits with a device known as a Josephson Photomultiplier (JPM), which crucially stores the result of a qubit measurement in a classical circulating supercurrent within the device and allows for integration with SFQ detection circuitry. This technique is experimentally demonstrated, with single-shot measurement fidelity of 92%. Two methods for accessing this measurement result are presented, one utilizing ballistic fluxons, and another utilizing flux comparison. Initial experimental results of the latter are presented. In addition, I describe a scheme for controlling qubits with sequences of digital SFQ pulses. This method is then used to control a qubit without a microwave signal generator, with results of an average single-qubit gate fidelity of around 95%. When combined, these techniques form a nearly fully digital interface to superconducting qubits, which could allow these systems to scale much more easily.
Single-flux-quantum (SFQ) digital circuitry has great potential in building a scalable control system of superconducting qubits. In this work, we describe a practical SFQ-based two-qubit gate for transmon qubits. The controlled-ZZZ (CZ) gate is activated by near-resonant SFQ-pulse trains near the target transition involving the second excited state. Numerical simulations show that the fidelity of a SFQ-activated CZ gate in excess of 99.9% is achievable within 100-ns gate time. We evaluate the CZ gate error caused by leakage and SFQ-pulse width. Combined with the proposed feasible expansion methods, this work is a supplement to the scalable and integratable superconducting-qubit control system based on SFQ digital logic.
The convergence of quantum computing and high-performance computing (HPC) necessitates innovative approaches to qubit control and coherence for scalable quantum systems. In this work, we explore the integration of superconducting Single-Flux Quantum (SFQ) digital circuits to enhance quantum state manipulation, leveraging their potential for high-speed, energy-efficient classical control. Our approach maps SFQ pulse trains and configurable SFQ-based switches to discrete phase shifts, enabling efficient qubit state transformations with minimal decoherence overhead. We introduce a classically driven SFQ-based quantum gate implementation, where SFQ pulses orchestrate the state evolution of qubits. To support dynamic and flexible qubit control within hybrid quantum-HPC architectures, we design and implement a multi-frequency SFQ pulse generator, capable of generating tailored pulse sequences that seamlessly interface with SQUID-based resonator-qubit cavities. This work demonstrates a promising path toward integrating quantum accelerators with classical HPC infrastructure, opti-mizing quantum-classical workflows, and enabling scalable, high-performance quantum computation.
In the interest of alleviating qubit coherence constraints and making quantum control circuits more efficient, this paper explores qubit control using superconducting Single-Flux Quantum (SFQ) digital circuits. By using SFQ pulse trains and SFQ switches, we represent qubit state transformations through their equivalent phase changes, where each SFQ pulse represents a phase change of certain degrees. We propose classical-based unitary quantum gates represented by SFQ pulses. We create a classical equivalent model for quantum gates based on an SFQ-based parametric pulse sequence equivalent to quantum Pauli gates. To generate pulse sequences of configurable parameters, we implement a versatile multi-frequency pulse generator that seamlessly integrates with the qubit-resonator cavity.
In the traditional approach to controlling superconducting qubits using microwave pulses, the field of pulse shaping has emerged in order to assist in the removal of leakage and increase gate fidelity. However, the challenge of scaling microwave control electronics has created an opportunity to explore alternative methods such as single-flux quantum (SFQ) pulses. For qubits controlled by SFQ pulses, high fidelity gates can be achieved by optimizing the binary control sequence. We extend the notion of the derivative removal by adiabatic gate (DRAG) framework a transmon qubit controlled by SFQ drivers. The proposed implementation of SFQ pulse sequences can be stored in 22 bits or fewer, with gate fidelities exceeding 99.99%. This modest memory requirement could help reduce the footprint of the SFQ coprocessors and power dissipation while preserving their inherent advantages of scalability and cost-effectiveness.