Noise in a microwave amplifier is limited by quantum particles of heat

November 10, 2014

As part of an international collaboration, scientists at Chalmers University of Technology have demonstrated how noise in a microwave amplifier is limited by self-heating at very low temperatures. The results will be published in the prestigious journal Nature Materials. The findings can be of importance for future discoveries in many areas of science such as quantum computers and radio astronomy.

Many significant discoveries in physics and astronomy are dependent upon registering a barely detectable electrical signal in the microwave regime. A famous example of this was the discovery of cosmic background radiation that helped confirm the Big Bang theory. Another example is the detection of data from scientific instruments in space missions on their way to distant planets, asteroids or comets.

Faint microwave signals are detected by transistor-based low-noise amplifiers. Researchers at Chalmers University of Technology have now optimised indium phosphide transistors using a special process for this purpose. A spin-off company from Chalmers, Low Noise Factory, designs and packages amplifier circuits.

"Cooling the amplifier modules to -260 degrees Celsius enables them to operate with the highest signal-to-noise ratio possible today," says Jan Grahn, Professor of microwave technology at Chalmers. "These advanced cryogenic amplifiers are of tremendous significance for signal detection in many areas of science, ranging from quantum computers to radio astronomy."

Using a combination of measurements and simulations, the researchers investigated what happens when a microwave transistor is cooled to one tenth of a degree above absolute zero (-273 degrees Celsius). It was thought that noise in the transistor was limited by so-called hot electrons at such extreme temperatures. However, the new study shows that the noise is actually limited by self-heating in the transistor.

Self-heating is associated with phonon radiation in the transistor at very low temperatures. Phonons are quantum particles that describe the thermal conductivity of a material. The results of the study are based on experimental noise measurements and simulations of phonons and electrons in the semiconductor transistor at low temperatures.

"The study is important for the fundamental understanding of how a transistor operates close to absolute zero temperature, and also how we should design even more sensitive low-noise amplifiers for future detectors in physics and astronomy," explains Jan Grahn.
-end-
The research has been performed as part of an international exchange between Chalmers University of Technology in Sweden and the California Institute of Technology. Co-authors are the University of Salamanca and the Swedish company Low Noise Factory. The study was conducted at the Gigahertz Centre, a joint venture between Chalmers, research institutes, company partners and the Swedish Governmental Agency for Innovation Systems (Vinnova).

Chalmers University of Technology

Related Quantum Computers Articles from Brightsurf:

Optical wiring for large quantum computers
Researchers at ETH have demonstrated a new technique for carrying out sensitive quantum operations on atoms.

New algorithm could unleash the power of quantum computers
A new algorithm that fast forwards simulations could bring greater use ability to current and near-term quantum computers, opening the way for applications to run past strict time limits that hamper many quantum calculations.

A new technique prevents errors in quantum computers
A paper recently published in Nature presents a protocol allowing for the error detection and the protection of quantum processors in case of qubit loss.

New method prevents quantum computers from crashing
Quantum information is fragile, which is why quantum computers must be able to correct errors.

Natural radiation can interfere with quantum computers
Radiation from natural sources in the environment can limit the performance of superconducting quantum bits, known as qubits.

New model helps to describe defects and errors in quantum computers
A summer internship in Bilbao, Spain, has led to a paper in the journal Physical Review Letters for Jack Mayo, a Master's student at the University of Groningen, the Netherlands.

The first intuitive programming language for quantum computers
Several technical advances have been achieved recently in the pursuit of powerful quantum computers.

Hot qubits break one of the biggest constraints to practical quantum computers
A proof-of-concept published today in Nature promises warmer, cheaper and more robust quantum computing.

Future quantum computers may pose threat to today's most-secure communications
Quantum computers that are exponentially faster than any of our current classical computers and are capable of code-breaking applications could be available in 12 to 15 years, posing major risks to the security of current communications systems, according to a new RAND Corporation report.

Novel error-correction scheme developed for quantum computers
Experimental quantum computers are plagued with errors. Here Dr Arne Grimsmo from the University of Sydney and colleagues from RMIT and the University of Queensland offer a novel method to reduce errors in a scheme applicable across different types of quantum hardware.

Read More: Quantum Computers News and Quantum Computers Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.