NIS Thermometer

The Technology

NIST scientists are developing a highly accurate thermometer that measures extremely low temperatures, ranging from a hundredth of a degree above absolute zero, or 0.01 kelvin, to 1 kelvin.

The device, small enough to fit on a chip, consists of three distinct layers: an ultrathin sheet of insulating material (“I”) sandwiched between a normal, or ordinary, metal (“N”) and a superconductor (“S”). Researchers therefore call the device the NIS thermometer.

This hybrid NIS sensor exploits a temperature-dependent quantum property known as electron tunneling, which allows electrons from the metal to flow or tunnel through the insulator into the superconducting layer. The magnitude of the tunneling current is exquisitely sensitive to the temperature of the normal metal, allowing researchers to determine its temperature with high accuracy.

The temperature of the thermometer provides information about the temperature of any material — such as a complex heterostructure in an optoelectronic device — that’s in thermal contact with the N layer.

Advantages Over Existing Technology

The NIS sensor is one of the first low-temperature thermometers that directly traces the kelvin, the base unit of temperature, to the International System of Units (SI). This ensures that low-temperature measurements are consistent, reliable and have a known relationship to the fundamental constants of nature.

NIS thermometers do not need to be calibrated by other instruments. They can either operate as standalone temperature sensors on a chip built by NIST or be directly fabricated on a customer’s chip, such as a quantum computing chip.

A complete system, including the sensor plus associated electronics, would cost less than half that of traditional resistance-based thermometers and would eliminate the need for regular calibrations. With further research and development, it should be possible to extend the temperature range of NIST thermometers to as low as 0.001 K and as high as 10 K.

Applications

Low-temperature thermometry plays a critical role in fields ranging from aerospace to quantum computing and sensing.

Quantum computers must be cooled to temperatures below 1 K in order for qubits, the fragile but fundamental units of quantum information, to function properly. Measuring and maintaining these low temperatures is paramount because even the tiniest temperature increase can disturb or destroy the quantum properties that allow qubits to rapidly perform complex computations.

The study of materials and phenomena at extremely low temperatures, known as cryogenics, relies heavily on accurate low-temperature thermometers. Scientists use these sensors to study superconducting materials, quantum phenomena, and the behavior of matter near absolute zero.