Recently, scientists have achieved quantum error correction of diamond quantum memory for the first time under zero magnetic field.
The nitrogen-vacancy color center in the diamond acts as a quantum memory and automatically corrects errors through error-correcting coding, picture from Yokohama National University
Compared with traditional computers, scientists believe that quantum computers can operate thousands of times faster on specific complex problems and may enable innovation in chemistry, cryptography, finance, pharmaceuticals and other fields. As a result, scientists are looking for ways to build quantum computer networks. Among them, fault-tolerant quantum memory will play an important role, because it is still well responded to hardware and software failures.
When scientists manipulate quantum memory based on nuclear spin, a magnetic field is required. But magnetic fields hinder the integration of superconducting qubits. Qubits are the basic units of information storage in quantum computers, similar to binary bits in traditional computers.
A research group at Yokohama National University (YNU) in Japan is exploring a type of quantum memory that is fault-tolerant to operation or the environment. The team studied nitrogen-amputation center (NV center) in diamond (the rough of diamonds) to further develop fault-tolerant quantum computer technology.
NV color center is one of the most common point defects in diamond crystal structures and is currently the most representative quantum system. As an important quantum material, NV color centers are solid-state devices at the atomic level, with optically adjustable spin freedom, core functions such as qubits and quantum detectors in solid-state quantum processors, and are expected to play a role in a range of applications such as quantum computing.
This time, the team used a diamond nitrogen-ampere color center with two carbon isotope nuclei to prove quantum fault tolerance in quantum memory under zero magnetic field. The results were recently published in Communications Physics.
Carbon spin manipulation with magnetic and zero magnetic fields, picture from the paper
To scale up superconducting qubit-based quantum computers, the team had to work with zero magnetic fields. When the magnetic field changes, there are generally two kinds of errors that affect the qubits: bit flipping and phase flipping.
The team used a three-dimensional coil to counteract residual magnetic fields, including the geomagnetic field (a natural magnetic phenomenon present in the Earth's interior), and tested the quantum error correction of three qubits for bit flipping and phase flip errors under zero magnetic fields, proving that the aforementioned quantum memory is error-corrected and can be automatically corrected when errors occur.
Previous studies have focused on quantum fault tolerance under relatively strong magnetic fields, and the Yokohama National University research group has shown for the first time quantum manipulation of electron and nuclear spins without magnetic fields.
A quantum circuit of three qubits for quantum error correction (QEC) to correct bit flip (a) and phase flip (b) errors, picture from the paper
"Quantum error correction makes quantum memory fault-tolerant to operations or the environment without the need for magnetic fields, and opens the way for distributed quantum computing, as well as quantum networks with storage-based quantum interfaces or repeaters." Hideo Kosaka, a professor at Yokohama National University and the paper's lead author, said.
The above results can be applied to the construction of large-scale distributed quantum computers and long-distance quantum communication networks, such as connecting superconducting qubits, quantum memory based on nuclear spin and other quantum systems that are susceptible to magnetic fields.
In the future, the team plans to further expand the research technology. Kosaka said, "We want to develop a quantum interface between superconductivity and photon quantity bits to enable large-scale fault-tolerant quantum computers." ”