Researchers use laser light and single-photon measurements to take important steps toward producing quantum states of sound inside a small device.
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Laser
light (red) propagates in a tapered optical fiber and is coupled into a
whispering-gallery-mode microresonator where it circulates up to a million
times. As the light circulates it interacts with high-frequency acoustic waves.
Credit: Jack Clarke |
Researchers all over the world can now generate and manipulate quantum states in a wide range of physical systems, from single light particles to complex molecules with hundreds of atoms. This control is allowing for the development of powerful new quantum technologies like quantum computers and quantum communications, as well as fascinating new ways to test quantum physics' foundations. A major contemporary difficulty is figuring out how to construct quantum states on a bigger scale, which will allow quantum physics' technological potential to be realised and its boundaries to be explored.
Imperial
College London, the University of Oxford, the Niels Bohr Institute, the Max
Planck Institute for the Science of Light, and Australian National University
collaborated to create and study non-Gaussian states of high-frequency sound
waves with over a trillion atoms. A randomly changing sound field in thermal
equilibrium is transformed into a pattern thrumming with a more specified
magnitude by the team.
This study
makes significant progress toward generating more macroscopic quantum states,
which will enable the development of future quantum internet components and the
testing of quantum mechanics' boundaries. The team's findings have been
published in the journal Physical Review Letters.
"We confine laser light to circulate inside a micro-scale resonator to conduct this research. In what's known as a whispering-gallery mode, light can circulate up to a million times around the edge of this tiny structure "Imperial University's John Price, a co-first author on the paper, explains.
"As the light circulates, it interacts with high-frequency sound waves, and we can use the laser light to both generate and define intriguing acoustic states," says Imperial co-first author Andreas Svela.
"Then, when we notice a single photon created by this light-sound interaction, the detection event gives us the indication that we've created our target state," says Imperial's Lars Freisem, co-first author.
A single
photon indicates that a single phonon—a particle of sound energy—has been
subtracted from the acoustic field's original condition. The team has
previously investigated single-phonon addition and subtraction, observing a
counterintuitive doubling of the average number of sound quanta, but the
current work goes a step further by precisely characterizing the fluctuations
of the sound wave generated and observing the non-Gaussian pattern that results.
"Generating
non-Gaussian quantum states is important for research in quantum information
and physics foundations, and this research excitingly brings us closer to
generating such states at a macroscopic scale using sound fields," says
co-first author Georg Enzian, who is now working at the Niels Bohr Institute in
Copenhagen.
"Future
work based on this approach could pave the way for a feasible way to store and
retrieve quantum data in a coherent manner. To put it another way, create a
quantum RAM for a quantum computer. Furthermore, studies like this can provide
much-needed insight into the various mechanisms that cause quantum phenomena to
decay and become classical "Principal investigator Michael Vanner of
Imperial College's Quantum Measurement Lab.
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