Physicists at the University of Virginia’s College of Arts & Sciences have demonstrated a breakthrough in the creation of massive numbers of entangled qubits — more precisely, a multilevel variant called “Qmodes.”

The physicists used an optical parametric oscillator (a laser) that emits entangled quantum electromagnetic fields (the Qmodes) over a rainbow of equally spaced colors called an “optical frequency comb.” Ultrastable lasers emitting over an optical frequency comb have revolutionized the science of precision measurements, called metrology, and paved the way to multiple technological breakthroughs.

They engineered 15 groups of four entangled Qmodes each, for a total of 60 measurable Qmodes, the most ever created. They believe they may have created as many as 150 groups, or 600 Qmodes, but could measure only 60 with the techniques they used.

Each Qmode is a sharply defined color of the electromagnetic field. In lieu of a coin toss measurement, the Qmode measurement outcomes are the number of quantum particles of light (photons) present in the field. Hundreds to thousands of Qmodes would be needed to create a quantum computer, depending on the task.

“With this result, we hope to move from this multitude of small-size quantum processors to a single, massively entangled quantum processor, a prerequisite for any quantum computer,” said Olivier Pfister, professor of physics.

Ref.: Matthew Pysher, et al., Parallel Generation of Quadripartite Cluster Entanglement in the Optical Frequency Comb, Physical Review Letters, 2011; 107 (3) [DOI: 10.1103/PhysRevLett.107.030505]