Scientists gauge quantum states for chip cooling, settling

Scientists took great pains not to disturb the coherence of quantum states through constant measurements. Israeli and German scientists recently collaborated to turn this technique on its head, using the measurement of quantum states to control thermodynamics (temperature) and entropy (settling).

The scientists noted that in two-level quantum systems, like those used to represent qbits, which are the frequency used to measure the states, these might control both temperature and entropy. The approach enables novel cooling schemes as well as instant settling for atomic, molecular and solid-state devices.

The scientists at the Weizmann Institute in Israel and Potsdam University in Germany claimed that the constant that controls thermodynamics and entropy is the frequency used to measure their quantum states. Both cooling and state purification, according to them, can be made to occur much more quickly than the normal time needed to achieve thermal equilibrium, cooling or feedback around a control loop.

Quantum measurements are intrusive, according to Gershon Kurizki, professor; Noam Erez, postdoctoral fellow; and Goren Gordon, doctoral candidate, Wiesmann Institute. They worked in collaboration with Mathias Nest, researcher, Potsdam University.

Classical measurements do not interfere with the system being measured. When a specific measurement is made in a quantum system, however, the coupling to other specific systems is interrupted temporarily by the measurement.

This odd characteristic of quantum mechanics can be harnessed, according to the scientists, as a new method of chip-scale cooling and quantum computing. Engineers usually measure heat loss in terms of the size of the heat sink needed to cool a chip. But the researchers claimed that ultrafast measurements can speed up or slow down thermal effects independent of the size of the heat sink.

By adjusting the rate at which optical temperature measurements were made, the researchers found that the temperature itself could be adjusted.

"Taking frequent measurements also changed the system entropy or relaxation time—the needed time to reach the lowest energy state. By adjusting system entropy, future quantum computers could tilt toward faster settling of intermediate results and faster resetting between calculations," they said.

- R. Colin Johnson
EE Times