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Microwave amplifier for quantum electronics

Superconducting tunnel junction circuit allows broadband parametric amplification of very weak microwave signals

PTB-News 3.2017
Especially interesting for

fundamental research

electrical quantum technologies

quantum information processing

Quantum information technology requires low-noise and extreme broadband amplifiers for weak microwave signals. A novel parametric amplifier with Josephson junctions that was developed at PTB distinguishes itself through high gain, broad bandwidth and low noise.

Chip mit supraleitender SQUID-Serienschaltung des Wanderwellenverstärkers im Probenhalter mit Mikrowellenanschlüssen. Die Serienschaltung enthält 2296 SQUIDS in einer 11,5 cm langen mäanderförmigen Hochfrequenzleitung.

A parametric amplifier is a low-noise high-frequency amplifier which converts energy from a pump into a signal wave by means of nonlinear, reactive components. Modern parametric amplifiers with Josephson junctions (Josephson parametric amplifiers – JPAs) exhibit almost quantum-limited noise behavior, but due to their resonance architecture, they cannot attain sufficiently broad bandwidths. These are, however, urgently required for ultrasensitive microwave sensors (for the detection of microwave signals on the order of single photons) or for the development of quantum computers. In contrast, JPAs based on so-called traveling waves can achieve broad bandwidths. To date, these traveling-wave JPAs have been realized by Josephson junctions that were embedded in high-frequency lines, whereby the relation between the Josephson current and its phase (the so-called Josephson nonlinearity) is given by a cubic relation.

A new concept for a simple set-up of a traveling-wave JPA based on an advantageous quadratic Josephson nonlinearity has now been suggested at PTB. This approach is based on single-junction SQUIDs connected in series; it allows the Josephson nonlinearity to be controlled by means of an external magnetic field. In contrast to JPAs with a cubic nonlinearity, it is possible to efficiently adjust the phases of the traveling pump wave and of the signal wave to be amplified by suitably selecting the operating point. This leads to a larger gain of the amplifier in a broad frequency range. Moreover, the useful signal can easily be separated, since it is much better distinguished from the pump signal in the frequency range.

An initial test circuit was manufactured using the niobium technology with Nb/AlOx/Nb Josephson junctions; it was then characterized in liquid helium at a temperature of 4.2 K. The measurements show a power gain of more than 10 dB in a frequency range of approx. 3 GHz. Further investigations of the JPA circuit will show whether the minimum amplifier noise aimed for can be achieved at the quantum-mechanical limit. For a possible later use in quantum electronics, however, gain and bandwidth need to be further increased.


Ralf Dolata
Department 2.4
Quantum Electronics
Phone: +49 (0)531 592-2247
Opens window for sending emailralf.dolata(at)ptb.de

Scientific publication

A. B. Zorin: Josephson traveling-wave parametric amplifier with three-wave mixing. Phys. Rev. Applied 6, 034006 (2016)