A fast quantum interface between different spin qubit encodings

TL;DR

This paper introduces a hybrid quantum system combining LD and ST spin qubits, enabling fast, tunable interactions and a rapid controlled-phase gate, advancing scalable quantum computing.

Contribution

It presents a novel hybrid architecture with a fast, electrically tunable quantum interface between different spin qubit encodings, demonstrating a rapid controlled-phase gate.

Findings

Controlled-phase gate achieved in 5.5 ns

Dephasing time measured at 211 ns

Hybrid system leverages advantages of both qubit types

Abstract

Single-spin qubits in semiconductor quantum dots proposed by Loss and DiVincenzo (LD qubits) hold promise for universal quantum computation with demonstrations of a high single-qubit gate fidelity above 99.9 % and two-qubit gates in conjunction with a long coherence time. However, initialization and readout of a qubit is orders of magnitude slower than control, which is detrimental for implementing measurement-based protocols such as error-correcting codes. In contrast, a singlet-triplet (ST) qubit, encoded in a two-spin subspace, has the virtue of fast readout with high fidelity and tunable coupling to the electric field. Here, we present a hybrid system which benefits from the different advantages of these two distinct spin-qubit implementations. A quantum interface between the two codes is realized by electrically tunable inter-qubit exchange coupling. We demonstrate a controlled-phase (CPHASE) gate that acts within 5.5 ns, much faster than the measured dephasing time of 211 ns. The presented hybrid architecture will be useful to settle remaining key problems with building scalable spin-based quantum computers.