Two-qubit logical operations in three quantum dots system

TL;DR

This paper proposes a fast, electrically controlled two-qubit gate system using three quantum dots, enabling key quantum operations within nanoseconds, suitable for fault-tolerant quantum computing.

Contribution

It introduces a novel method for implementing multiple quantum gates in a three-dot system with minimal electrical pulses and analyzes its robustness against environmental effects.

Findings

Single-pulse $CPHASE$ gate achieved in 2.3 ns

Optimal configurations for $CNOT$, $QFT$, and $SWAP$ identified

System shows potential for fault-tolerant quantum computation

Abstract

We consider a model of two interacting always-on, exchange-only qubits for which controlled phase ($CPHASE$), controlled NOT ($CNOT$), quantum Fourier transform ($QFT$) and $SWAP$ operations can be implemented only in a few electrical pulses in a nanosecond time scale. Each qubit is built of three quantum dots (TQD) in a triangular geometry with three electron spins which are always kept coupled by exchange interactions only. The qubit states are encoded in a doublet subspace and are fully electrically controlled by a voltage applied to gate electrodes. The two qubit quantum gates are realized by short electrical pulses which change the triangular symmetry of TQD and switch on exchange interaction between the qubits. We found an optimal configuration to implement the $CPHASE$ gate by a single pulse of the order 2.3 ns. Using this gate, in combination with single qubit operations, we searched for optimal conditions to perform the other gates: $CNOT$, $QFT$ and $SWAP$. Our studies take into account environment effects and leakage processes as well. The results suggest that the system can be implemented for fault tolerant quantum computations.