Measuring quantum states could yield new chip-cooling scheme

PORTLAND, Ore. — Scientists take 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 claim that in two-level quantum systems--like those used to represent quantum bits (q-bits)--the frequency used to measure them controls both temperature and entropy. The approach could enable novel cooling schemes as well as instant-settling for atomic, molecular and solid-state devices.

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

Quantum measurements are intrusive, according to professor Gershon Kurizki, postdoctoral fellow Noam Erez and doctoral candidate Goren Gordon at the Wiesmann Institute. They worked in cooperation with researcher Mathias Nest at 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 temporarily interrupted by the measurement.

This odd characteristic of quantum mechanics can be harnessed, according to these 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 claim that ultra-fast 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 time needed 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, the researchers said.