Neutral atom quantum computer announces record coherence time
Coherence Times is one of the important indicators of the quality of qubits. It represents the time that qubits can maintain a quantum state (external environmental interference will destroy the quantum state). Under the condition of a certain calculation time, the longer the coherence time, the longer the coherence time. The more calculations a quantum computer can do. Therefore, achieving longer coherence times is a common goal in the field of quantum computing.
On May 20, researchers at Atom Computing reported their latest record for coherence times — 100,000 times faster — on its 100+ qubit neutral atom quantum computer, Phoenix. The research results were published in the journal Nature Communications under the title "Assembly and Coherent Control of Nuclear Spin Qubit Registers" [1].
We know that the coherence time includes relaxation time T1 and lifetime T2. In experiments, Phoenix's T2 was 40±7 seconds—the team says this is the longest coherence time ever on a commercial platform. T1 is almost infinite.
Longer coherence times offer quantum computers a number of advantages, according to the research team. "This is important because longer coherence times mean fewer constraints on running deep circuits, and more time for error correction schemes to detect and correct errors through intermediate circuit measurements [2]."
Achieving Long Coherence Time Requirements The qubit interacts with the environment minimally, but this requirement often comes with a drawback: Typically, the weaker the qubit's interaction with the environment, the harder it is to connect the qubit to the necessary components used to drive the execution of quantum computations. , the interaction of the control field coupling.
The researchers overcome this shortcoming by choosing neutral atom-based qubits and single-qubit control via a software-configurable dynamic laser. The dynamic lasers described above can be guided and driven with sub-micron spatial precision and sub-microsecond temporal precision.
Ramsey-echo (Ramsey-echo) measurements performed on an array of 21 qubits exhibited high contrast over tens of seconds, indicating T2echo = 40 ± 7 seconds. The team says this is the longest coherence time ever demonstrated on a commercial platform.
Specifically, the software-configurable optical control scheme developed by the research team enables Phoenix to simultaneously drive arbitrary single-quantum gate operations for all qubits within a single column or row, while maintaining long coherence times.
Phoenix experimental architecture diagram. The qubits are trapped in a vacuum chamber and controlled through a high numerical aperture microscope objective using a software-configurable dynamic laser. Reading is performed by collecting scattered light onto a camera through the same microscope objective.
In the above neutral atomic model, Phoenix encodes quantum information—the qubit states |0> and |1>, in the two nuclear spin states of an uncharged strontium atom. This type of encoding offers two key advantages: The first advantage of nuclear spin states is that, since both qubit states exist in the electronic ground state, the time it takes for one state to spontaneously decay to the other (again The spin relaxation time T1) is called practically infinite.
The spin relaxation time, called T1, describes the time it takes for one qubit state to spontaneously decay to another. A short T1 will appear as a line that starts near 1 and drifts down. There is no significant downward drift in the measurement results of this study, which indicates that the experimental spin relaxation time is much longer than the longest measurement time.
A second key advantage of nuclear spin qubits is that, because the qubit states have such similar energies, they are affected almost equally by external fields. "This means that perturbations, such as those caused by externally applied induced light, will affect both qubit states in the same way," the researchers explained. Since these perturbations are common-mode, they do not affect the system as a whole. coherence. This feature essentially enables our world-record coherence time." The paper also summarizes several technical steps in building large-scale commercial quantum computers, including: long coherence times, driving arbitrary single quantum The ability to manipulate bits, and capture 100+ qubits, the researchers believe will be greatly improved in the future.
"As we develop second-generation quantum computers, we will build on Phoenix's proven architecture and success by scaling up to systems with high fidelity and qubit counts high enough to solve problems that classical computers cannot," the company said. Problem solved."
Reference link:
[1]https://www.nature.com/articles/s41467-022-29977-z
