Deep-well ultrafast manipulation of a SQUID flux qubit

TL;DR

This paper demonstrates ultrafast manipulation of a superconducting flux qubit using magnetic flux pulses, achieving sub-nanosecond oscillations and comparable coherence times to microwave methods, with potential for faster quantum control.

Contribution

It introduces a novel flux pulse technique for qubit manipulation, enabling ultrafast control without microwave pulses, and discusses its advantages and future applications.

Findings

Achieved sub-nanosecond coherent oscillations (50-200 ps).

Coherence time up to 10 ns comparable to microwave methods.

Presented feedback control to mitigate slow fluctuations.

Abstract

Superconducting devices based on the Josephson effect are effectively used for the implementation of qubits and quantum gates. The manipulation of superconducting qubits is generally performed by using microwave pulses with frequencies from 5 to 15 GHz, obtaining a typical operating clock from 100MHz to 1GHz. A manipulation based on simple pulses in the absence of microwaves is also possible. In our system a magnetic flux pulse modifies the potential of a double SQUID qubit from a symmetric double well to a single deep well condition. By using this scheme with a Nb/AlOx/Nb system we obtained coherent oscillations with sub-nanosecond period (tunable from 50ps to 200ps), very fast with respect to other manipulating procedures, and with a coherence time up to 10ns, of the order of what obtained with similar devices and technologies but using microwave manipulation. We introduce the ultrafast manipulation presenting experimental results, new issues related to this approach (such as the use of a feedback procedure for cancelling the effect of "slow" fluctuations), and open perspectives, such as the possible use of RSFQ logic for the qubit control.