Error-prone qubits could correct themselves

This artist’s conception simplifies the ideas in the paper to illustrate the new qubit design’s overall concept. Photons flow continuously into the cavity like water flowing down a stream (#1), and the photons' wavelike natures interact with one another as an interference pattern, forming a superposition of the values 0 and 1 and storing them as the qubit’s information (#2). Noise represented by the log falling into the stream (#3) can easily destroy an ordinary qubit’s interference pattern, but refreshing the photons keeps the source of the waves strong, allowing the pattern to reestablish itself (#4) in short order, thereby keeping the qubit’s information robust against some common threats. Credit: B. Hayes/NIST

Physicists from the National Institute of Standards and Technology (NIST), the University of Maryland and the California Institute of Technology may have found a way to design quantum memory switches that would self-correct.

The team’s theory suggests an easier path to creating stable qubits, which ordinarily are subject to environmental disturbances and errors. Finding methods of correcting these errors is a major issue in quantum computer development, but the research team’s approach to qubit design could sidestep the problem.

Designers are experimenting with many approaches to building qubits. One promising architecture is called a photonic cavity resonator. Within its tiny volume, multiple photons can be driven to bounce back and forth between the cavity’s reflective walls. The photons, manifesting their wavelike properties in the cavity, combine to form ripple-like interference patterns. The patterns themselves contain the qubit’s information. It’s a delicate arrangement that, like ripples on a pond’s surface, tends to dissipate quickly. 

It is also easily perturbed. To work, qubits need peace and quiet. Noise from the surrounding environment—such as heat or magnetic fields emitted by other nearby components—can disturb the interference pattern and ruin the calculation.

Rather than construct an elaborate system to detect, measure and compensate for noise and errors, the team members perceived that if the supply of photons in the cavity is constantly refreshed, the qubit’s quantum information can withstand certain amounts and types of noise.

The proposed method adds to an arsenal of promising quantum computer error-correction techniques, such as “topological” qubits, which would also be self-correcting but require yet-to-be-made exotic materials. While the team expects the new approach to be particularly useful for quantum computing based on microwave photons in superconducting architectures, it might also find applications in computing based on optical photons. (NIST)

The paper has been published in Physical Review Letters.

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