Journal Article

A two-qubit logic gate in silicon

Huang, W., Hwang, J. C. C., Morello, A., Simmons, S., Veldhorst, M., Dehollain, J. P., Hudson, F. E., Muhonen, J. T., Laucht, A., Itoh, K. M., Dzurak, A. S., Yang, C. H.

2015

Overview

A high-fidelity two-qubit CNOT logic gate is presented, which is realized by combining single- and two-qubit operations with controlled phase operations in a quantum dot system using the exchange interaction. A silicon CNOT logic gate Whilst many different types of quantum bit or qubit have been realized, there are compelling reasons to focus on the development of silicon-based qubits that can be easily integrated with the CMOS (complementary metal-oxide-semiconductor) semiconductor technology used in today's transistors and microchips. High-fidelity silicon qubits have been demonstrated, but until now they have not performed quantum logic operations. Menno Veldhorst et al . report a high-fidelity two-qubit controlled NOT (or CNOT) logic gate using spins in enriched silicon. This device is a step towards a scalable, solid-state platform for quantum computation. Quantum computation requires qubits that can be coupled in a scalable manner, together with universal and high-fidelity one- and two-qubit logic gates 1 , 2 . Many physical realizations of qubits exist, including single photons 3 , trapped ions 4 , superconducting circuits 5 , single defects or atoms in diamond 6 , 7 and silicon 8 , and semiconductor quantum dots 9 , with single-qubit fidelities that exceed the stringent thresholds required for fault-tolerant quantum computing 10 . Despite this, high-fidelity two-qubit gates in the solid state that can be manufactured using standard lithographic techniques have so far been limited to superconducting qubits 5 , owing to the difficulties of coupling qubits and dephasing in semiconductor systems 11 , 12 , 13 . Here we present a two-qubit logic gate, which uses single spins in isotopically enriched silicon 14 and is realized by performing single- and two-qubit operations in a quantum dot system using the exchange interaction, as envisaged in the Loss–DiVincenzo proposal 2 . We realize CNOT gates via controlled-phase operations combined with single-qubit operations. Direct gate-voltage control provides single-qubit addressability, together with a switchable exchange interaction that is used in the two-qubit controlled-phase gate. By independently reading out both qubits, we measure clear anticorrelations in the two-spin probabilities of the CNOT gate.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 142/126 / 639/766/483/481 / 639/925/357/1017 / 639/925/927/481 / Gates / Gates (Electronics) / Humanities and Social Sciences / Isotopic enrichment / letter / Magnetic fields / Materials / multidisciplinary / Quantum computing / Quantum dots / Quantum theory / Science / Science (multidisciplinary) / Semiconductors / Silicon / Transistors