Advancing Quantum Computing: Extending Coherence Time for Charge Qubits

Coherence stands as a pillar of effective communication, whether it is in writing, speaking, or information processing. This principle extends to quantum bits or qubits, the building blocks of quantum computing.

A Quantum Leap in Coherence Time

A team led by the U.S. Department of Energy’s (DOE) Argonne National Laboratory has achieved a significant milestone toward future quantum computing. 

They have extended the coherence time for their novel type of qubit to an impressive 0.1 milliseconds—nearly a thousand times better than the previous record. The research was published in Nature Physics.

Unveiling the Potential of Charge Qubits

In everyday life, 0.1 milliseconds is as fleeting as a blink of an eye. However, in the quantum world, it represents a long enough window for a qubit to perform thousands of operations. 

Unlike classical bits, qubits seemingly can exist in both states, 0 and 1. For any working qubit, maintaining this mixed state for a sufficiently long coherence time is imperative.

The Challenge of Coherence and Charge Qubits

The challenge is safeguarding the qubit against the constant barrage of disruptive noise from the surrounding environment. The team’s qubits encode quantum information in the electron’s emotional (charge) states, known as charge qubits.

“Among various existing qubits, electron charge qubits are especially attractive because of their simplicity in fabrication and operation, as well as compatibility with existing infrastructures for classical computers,” said Jin, the lead investigator of the project. “This simplicity should translate into low cost in building and running large-scale quantum computers.”

The Neon Platform and Quantum Protection

The team’s qubit is a single electron trapped on an ultraclean solid-neon surface in a vacuum. The neon is important because it resists disturbance from the surrounding environment.

Neon is one of a handful of elements that do not react with other elements. The neon platform keeps the electron qubit protected and inherently guarantees a long coherence time.

Toward Scalability and Quantum Entanglement

Following continued experimental optimization, the team not only improved the quality of the neon surface but also significantly reduced disruptive signals. 

Their work paid off with a coherence time of 0.1 milliseconds, about a thousand-fold increase from the initial 0.1 microseconds.

A Quantum Milestone: Scalability and Entanglement

The long lifetime of their electron qubit allows them to control and read out the single qubit states with very high fidelity. 

Yet another important attribute of a qubit is its scalability to link with many other qubits. The team achieved a significant milestone by showing that two-electron qubits can couple to the same superconducting circuit, marking a pivotal stride toward two-qubit entanglement, a critical aspect of quantum computing.

Continuing the Quantum Journey

The team still needs to optimize their electron qubit fully and will continue to work on extending the coherence time even further, as well as entangling two or more qubits. 

This research collaboration involves multiple institutions, including Lawrence Berkeley National Laboratory, Massachusetts Institute of Technology, Northeastern University, Stanford University, the University of Chicago, and the University of Notre Dame.

Read the original article on PHYS.

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