What it means for lasers.

Lasers are omnipresent. Quantum scientists
use them to control qubits in quantum computers; doctors use them to correct eyesight, and cashiers scan your groceries with
them. Current lasers are massive and
inefficient. Quantum scientists work at severely low temperatures on rather
small scales, and for over 40 years have been looking for an accurate and
efficient microwave laser to suit the
cold environment.


But now, Leo Kouwenhoven and a team at Delft
University of Technology unveiled an on-chip microwave laser based on
superconductivity. To make this possible, they installed a tiny section of an
uninterrupted superconductor, a Josephson junction (JJ) – consisting of two
superconductors coupled by a weak link – in an engineered on-chip cavity.

Dutch physicist Heike Kamerlingh Onnes
identified that materials transition to a superconducting state at extremely
low temperatures, letting electrical current flow without losing any energy.
The Josephson effect is a critical
application of superconductivity, because
if a short barrier interrupts a piece of
superconductor, electrical exporters run through a non-superconducting material
through quantum laws. The frequency they run through can be varied by an
externally applied DC voltage, making it an ideal perfect voltage to light

Lasers can emit perfectly corresponding
light, meaning the linewidth is very narrow. The introduction of the new
on-chip microwave laser allows for applications where microwave radiation with
little dissipation is crucial. Standardly, lasers are made from a significant number of atoms, molecules, or
semiconducting carriers inside the cavity. The layers are often not efficient
and deplete a significant amount of heat
when lasing, making it hard to operate in
low-temperature environments.

To create the Josephson junction laser, the
scientists connected a Josephson junction to a superconducting micro-cavity, so
minuscule – no larger than an ant.
Similar to a single atom, the Josephson junction corresponds with the cavity
like two mirrors for microwave light. After a small DC voltage is applied, the junction emits microwave photons on vibration
with the frequency of the cavity. The photons alternate back and forth between
two superconducting mirrors and force the Josephson junction to release more
photons coordinating with the photons in the cavity.

When the scientists cooled the device down to
very low temperatures and applied a small
DC voltage to the Josephson junction, they noticed an array of microwave
photons emitted at the output of the cavity. Since the on-chip laser is created
entirely from superconductors, it is extremely energy efficient and much more
stable than prior lasers. The device uses less than a picoWatt of power to
operate, a figure more than 100 billion times less than a light globe.

Current microwave sources are costly and ineffective;
the Josephson laser, on the other hand, is energy efficient and provides an
on-chip solution that is simple to modify and control. Looking to the future, this new on-chip microwave laser could
produce amplitude-squeezed light that has smaller intensity variances compared
to traditional lasers, which is crucial in many quantum communication customs.

Via Phys.org