Quantum computing: Superconducting qubits have passed a key quantum test

For the first time, a superconducting circuit has passed the Bell test, the highest test in physics for confirming the quantum behavior of a system. These circuits are used in quantum computers and this test proves that the qubits are indeed entangled.

When two particles are entangled, measuring the property of one will instantly affect the measured property of the other in a phenomenon called non-local correlation. For this to happen means that the entanglement effect must travel faster than light. This strange quantum effect test is called Bell’s inequality, and it sets a limit on how often particles happen to be in the same state in the absence of any real entanglement. Violation of Bell’s inequality is evidence that the pair of particles is indeed entangled.

Bell tests have been performed on many systems, but never on superconducting circuits. The test requires that the two entangled systems are far enough apart that the signal does not travel between them at the speed of light in the time it takes to measure both systems. This is difficult to test with superconducting circuits, as the whole thing must be kept at a temperature close to absolute zero. first time, Simon Stoltz PhDs from the Swiss Federal Institute of Technology in Zurich have successfully performed a bell test on such a circuit.

They connected two intertwined pieces of circuitry, called qubits or qubits, using microwaves sent through a 30-meter cooled aluminum tube, and stored each qubit in a separate refrigerator. . A random number generator was then used to determine what measurements to make on the qubits to avoid human bias.

The researchers made over 4 million measurements at a rate of 12,500 measurements per second. This is faster than light travels in the tube between her two qubits, and is the speed required to ensure that each pair is measured. Analyzing all these data points together yields high confidence that, as expected, Bell’s inequality is violated, and that qubits are indeed what Albert Einstein called “eerie behavior at a distance.” I understand.

“This test confirms the platform’s ability to leverage these unique quantum capabilities for technical applications,” said Storz. His success in connecting qubits across 30 meters holds particular promise for quantum computing and cryptography, he says. “This is a potential avenue for scaling up superconducting circuit-based quantum computers, for example in centers like future quantum supercomputers.”