Can you prove whether a large quantum system truly behaves according to the weird and wonderful rules of quantum mechanics—or if it just looks like it does? In a new study, physicists from Leiden, Beijing and Hangzhou found the answer to this question.

You could call it a “quantum lie detector”: Bell’s test designed by famous physicist John Bell. This test shows whether a machine, like a quantum computer, is truly using quantum effects or just mimics them.

As quantum technologies become more mature, ever more stringent tests of quantumness become necessary. In this new study, the researchers took things to the next level, testing Bell correlations in systems with up to 73 qubits—the basic building blocks of a quantum computer.

Macquarie University researchers have demonstrated a technique to dramatically narrow the linewidth of a laser beam by a factor of over ten thousand—a discovery that could revolutionize quantum computing, atomic clocks and gravitational wave detection.

In research published in APL Photonics, the team described using diamond crystals and the Raman effect—where laser light stimulates vibrations in materials and then scatters off those vibrations—to narrow the linewidth of laser beams by factors exceeding 10,000.

Laser linewidth measures how precisely a beam of light maintains its frequency and color purity. The narrower the linewidth, the more monochromatic and spectrally pure the laser. The team’s theoretical predictions suggest even greater improvements are possible with the method they have developed.

In a milestone for scalable quantum technologies, scientists from Boston University, UC Berkeley, and Northwestern University have reported the world’s first electronic–photonic–quantum system on a chip, according to a study published in Nature Electronics.