Josephson-Junction Qubits with Controlled Couplings

TL;DR

This paper proposes an improved Josephson-junction qubit design using controllable SQUIDs, enabling precise two-qubit coupling control and reducing operational errors for quantum computing.

Contribution

It introduces a new nano-electronic qubit design with controllable SQUIDs that simplifies coupling control and enhances quantum operation reliability.

Findings

The new design allows exact switching of two-qubit interactions.

It relaxes timing and parameter precision requirements.

Phase coherence times are sufficient for multiple operations.

Abstract

Low-capacitance Josephson junctions, where Cooper pairs tunnel coherently while Coulomb blockade effects allow the control of the total charge, provide physical realizations of quantum bits (qubits), with logical states differing by one Cooper-pair charge on an island. The single- and two-bit operations required for quantum computation can be performed by applying a sequence of gate voltages. A basic design, described earlier [cond-mat/9706016], is sufficient to demonstrate the principles, but requires a high precision time control, and residual two-bit interactions introduce errors. Here we suggest a new nano-electronic design, close to ideal, where the Josephson junctions are replaced by controllable SQUIDs. This relaxes the requirements on the time control and system parameters substantially, and the two-bit coupling can be switched exactly between zero and a non-zero value for arbitrary pairs. The phase coherence time is sufficiently long to allow a series of operations.