By Josh Perry, Editor
[email protected]

Researchers at Syracuse (N.Y.) University and the University of Wisconsin – Madison have developed a new technique for measuring the state of qubits in a quantum computer, according to a recent report from Syracuse.

Britton Plourde in his lab at Syracuse University. (Syracuse University)

Qubits exist in superpositions of two states (zero and one), rather than the single state of digital bits in standard computers. Coupled with entanglement (another feature of quantum mechanics), superposition gives researchers the idea that quantum algorithms can be developed for a variety of applications.

“Intensive, ongoing industrial-scale efforts by teams at Google and IBM have recently led to quantum processors with approximately 50 qubits,” the article explained. “These qubits consist of superconducting microwave circuits cooled to temperatures near absolute zero.”

Unfortunately, researchers believe that building a quantum computer will require upwards of several hundred qubits, if not more.

“The current state-of-the-art approach to measuring qubits involves low-noise cryogenic amplifiers and substantial room-temperature microwave hardware and electronics, all of which are difficult to scale up to significantly larger qubit arrays,” the article continued.

Syracuse researchers went a different direction and focused on the detection of microwave photons. This removed the need for a cryogenic amplifier and could eliminate the room-temperature hardware as well.

Researchers hope that this will lead to the scaled-up quantum processors with millions of qubits.

The research was recently published in Science. The abstract read:

“Fast, high-fidelity measurement is a key ingredient for quantum error correction. Conventional approaches to the measurement of superconducting qubits, involving linear amplification of a microwave probe tone followed by heterodyne detection at room temperature, do not scale well to large system sizes.

“We introduce an approach to measurement based on a microwave photon counter demonstrating raw single-shot measurement fidelity of 92%. Moreover, the intrinsic damping of the photon counter is used to extract the energy released by the measurement process, allowing repeated high-fidelity quantum nondemolition measurements.

“Our scheme provides access to the classical outcome of projective quantum measurement at the millikelvin stage and could form the basis for a scalable quantum-to-classical interface.”