Rapid single-flux quantum control of the energy potential in a double SQUID qubit circuit

Abstract

We report on the development and test of an integrated system composed of a flux qubit and a rapid single-flux quantum (RSFQ) circuit that allows qubit manipulation. The goal is to demonstrate the feasibility of control electronics integrated on the same chip as the qubit, in view of the application in quantum computation with superconducting devices. RSFQ logic relies on the storage and transmission of magnetic flux quanta and can be profitably used with superconducting qubits because of the speed, scalability, compatibility with the qubit fabrication process and low temperature environment. While standard RSFQ circuitry is well assessed, the application to quantum computing requires a complete rescaling of parameter values, in order to preserve the qubit coherence and reduce the power dissipation. In the system presented in this paper, the qubit role is played by a superconducting loop interrupted by a small dc SQUID, usually called a double SQUID, which behaves as a tunable rf-SQUID. Its energy potential has the shape of a double well, with the barrier between the wells controlled by magnetic flux applied to the inner dc SQUID. Here for the first time we report measurements at a base temperature of 370 mK in which flux control pulses with desired characteristics were supplied by a RSFQ circuit fabricated using non-standard parameters in the same chip as the qubit.

Optimal Qubit Control Using Single-Flux Quantum Pulses

“…Rapid single flux quantum (RSFQ) technology has been and is originally pursued as an ultra-high-speed classical computing platform [1,2]. The ability to generate reproducible identical pulses at a high clock rate has been demonstrated in integrated circuits [3]. Next to its original motivation of ultrafast digital circuits, this ability makes RSFQ technology a highly viable candidate for the on-chip generation of control pulses and readout for quantum computers based on Josephson devices [4][5][6][7][8][9].…”

Accurate Qubit Control with Single Flux Quantum Pulses

“…An obvious candidate for the cold control system is Single Flux Quantum (SFQ) digital logic, in which classical bits of information are stored in propagating fluxons, voltage pulses whose time integral equals the superconducting flux quantum Φ 0 = h/2e [5,6]. There have been experimental demonstrations of SFQbased circuits for qubit biasing [7][8][9], and fluxon-based schemes for qubit measurement have been proposed [10] and recently realized [11]. In addition, there has been a proposal to generate microwave pulses for qubit control by appropriately filtering SFQ pulse trains [12], although the required filter and matching sections would be challenging to realize practically.…”

Artificial neural network based on SQUIDs: demonstration of network training and operation

“…However there are different examples of important existing applications based on low temperatures and superconductivity (astrophysical detectors, medical imaging, high energy physics, quantum communication and computing, ultra low noise electronics, metrology and so on) where the introduction of superconducting electronics is not a cause of extra cost, but rather it could provide a natural interface between the superconducting system and the room temperature electronics, performing preliminary tasks such as multiplexing, pre-analysis and triggering [12][13][14][15]. In many cases the availability of a fast superconducting ANN close to the system could be a very useful and desirable tool.…”

“…Superconducting electronics allows computing speeds not possible with conventional semiconductor electronics (with clocks of the order of hundreds of Gigahertz) [9][10][11], but its drawback is the necessity to use cryogenic systems, with relative costs and request of competences. However there are different examples of important existing applications based on low temperatures and superconductivity (astrophysical detectors, medical imaging, high energy physics, quantum communication and computing, ultra low noise electronics, metrology and so on) where the introduction of a superconducting electronics is not cause of extra cost, but rather it could provide a natural interface between the superconducting system and the room temperature electronics, performing preliminary tasks such as multiplexing, pre-analysis and triggering [12][13][14][15]. In many cases the availability of a fast superconducting ANN close to the system could be a very useful and desirable tool.In the present work we consider a simple and flexible scheme for the realization of ANNs with SQUIDs (Superconducting Quantum Interference Devices), a widely used class of superconducting devices characterized by outstanding performances as ultrasensitive magnetometers and low noise amplifiers [16][17][18].…”