Experimental fault-tolerant universal quantum gates with solid-state spins under ambient conditions.

Xing Rong,Wenchao Ma,Yang Wu,Fazhan Shi,Ying Liu,Jiangfeng Du,Fei Kong,Jianpei Geng,Kebiao Xu,Zhen Jiang

doi:10.1038/ncomms9748

Abstract

Quantum computation provides great speedup over its classical counterpart for certain problems. One of the key challenges for quantum computation is to realize precise control of the quantum system in the presence of noise. Control of the spin-qubits in solids with the accuracy required by fault-tolerant quantum computation under ambient conditions remains elusive. Here, we quantitatively characterize the source of noise during quantum gate operation and demonstrate strategies to suppress the effect of these. A universal set of logic gates in a nitrogen-vacancy centre in diamond are reported with an average single-qubit gate fidelity of 0.999952 and two-qubit gate fidelity of 0.992. These high control fidelities have been achieved at room temperature in naturally abundant 13C diamond via composite pulses and an optimized control method.

Highlights

Quantum computation provides great speedup over its classical counterpart for certain problems
Further improvement of NV centre towards realistic quantum computation would require high fidelity quantum gates with errors below fault-tolerant threshold, which is proposed to be between 10 À 4 and 10 À 2 depending on the noise model and the computational overhead for realizing quantum gates[18,19,20]
Fault-tolerant control fidelity has been reported very recently in superconducting qubits[21], trapped ions[22] and phosphorus doped in silicons[23], it is still of great challenge to achieve fault-tolerant fidelity under ambient conditions, which is the case for NV centre in 13C naturally abundant diamond at room temperature

Summary

Results

We have improved a type of quantum optimal control method, named GRAPE (gradient ascent pulse engineering)[29], to design the CNOT gate which is robust against both d0 and d1. Because the nuclear spin is insensitive to the noise (such as fluctuations of the external magnetic field and the control RF field) and the CNOT gate designed by the quantum optimal control method consists of microwave pulses only, we can take into account the noise felt by the electron spin in the optimization procedures. The two peaks correspond to the nuclear spin qubit states jmI 1⁄4 0i and Fidelity

With CNOT

Discussion

Methods