Quantum computing: Superconducting qubits have passed a key quantum test

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

When two particles are entangled, measuring the property of one immediately affects the measured property of the other. This is called non-local correlation. When this happens, it means that the entanglement effect must travel faster than light. Set a limit on how often the same state occurs. Violations of Bell’s inequality are evidence that the pairs of particles are indeed entangled.

Bell tests have been performed on many systems, but not on superconducting circuits. In the test, the two entangled he systems must be far enough apart that the signal cannot 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. His Simon Storz and his colleagues at the Swiss Federal Institute of Technology in Zurich have successfully performed Bell’s test on such a circuit for the first time.

They used microwaves sent through a 30-meter-long cooled aluminum tube to connect two tangled parts of a circuit, called qubits or qubits, and put each qubit in a separate refrigerator. held to. A random number generator was then used to determine what kind of 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 the speed needed to ensure that each pair of measurements is taken faster than light travels down the tube between her two qubits. Analyzing all these data points together shows that, as expected, Bell’s inequality is violated, indicating that the qubits are indeed undergoing what Albert Einstein called “eerie effects at a distance.” I have found with a high degree of certainty that

“This test confirms that the platform can leverage these unique quantum capabilities for technical applications,” Storz said. The success of connecting qubits over 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 the future quantum supercomputer.”