Most quantum computing technologies rely on the ability to produce, manipulate and detect nonclassical light states. Nonclassical states are quantum states that cannot be produced directly with conventional light sources, such as lamps and lasers, and thus cannot be described by the theory of classical electromagnetism.
These unconventional states include compressed states, entangled states, and states with a negative Wigner function. The ability to similarly control the states of phononic systems dealing with acoustics and vibrations could open up interesting opportunities for the development of new quantum technologies, including quantum sensing devices and quantum information processing†
Researchers at TU Delft’s Kavli Institute of Nanoscience recently introduced a strategy that can be used to achieve a high level of control over phononic waveguides. This strategy, outlined in a paper published in Nature physicscould enable the use of phononic waveguides in quantum technology, similar to how optical fibers and waveguides are used today.
Optical fibers and waveguides can be used to transmit quantum information encoded in optical photons. In recent decades, they have been essential components for both quantum technology and classical communication technology.
“Realising components equivalent to optical fibers and waveguides for mechanical excitations has the potential to revolutionize the burgeoning field of quantum acoustics and phononics,” Simon Gröblacher, one of the researchers who conducted the study, said. to Phys.org. “Such low-loss phononic waveguides will not only enable and transmit (quantum) information encoded in phonons across tens of centimeters on a chip, but will provide the basis for complete coherent control over moving mechanical excitations.”
The main aim of the recent work of Gröblacher and his colleagues has been to devise a method for interpreting non-classical mechanical states in a phonic waveguide with individual phonons in a floating silicon microstructure. They ultimately aim to introduce a new toolbox to conduct experiments in quantum acoustics, allowing physicists and engineers to interact with quantum systems in new ways.
“Acoustic waves are fundamentally different from the oscillation of individual atoms or ions in traps, because of their associated large mass, their propagating nature and the ability to couple to a wide variety of other quantum systems such as quantum dots and superconducting qubits,” said Gröblacher. “Guiding single phonons is a critical step towards realizing hybrid quantum devices and transfer quantum information through heterogeneous networks.”
Gröblacher’s research group has conducted numerous experiments in recent years with an emphasis on phononic devices. In their previous studies, they were able to create, store and detect single phonons in photonic/phononic crystal devices, using optomechanical interactions between radiation and pressure.
As part of their recent study, they designed and realized the first phononic waveguide to produce non-classical moving mechanical excitations.
“By fabricating the waveguide from thin film silicon, we combined the waveguide with a source and detector for non-classical mechanical states and were able to verify the propagation of these quantum states in the waveguide,” explains Gröblacher. “This one acoustic waves at GHz frequencies are guided in a very constrained nanoscale geometry, with a long lifetime (up to a few milliseconds), especially at low temperatures, enabling the faithful transport of quantum states over centimeter distances on a chip.”
In their experiments, Gröblacher and his colleagues showed that when they propagate in their waveguide, the nonclassical correlations arising from phonons launched at different times are preserved. These non-classical correlations had a remarkable mechanical lifetime of about 100 s, meaning that their system could theoretically be used to emit single phonons over tens of centimeters, without significant energy losses.
The researchers also showed that their waveguide can be used to realize a phononic first-in-first-out (FIFO) quantum memory. In the future, such quantum memory could have valuable applications in telecommunications and quantum acoustics.
Amirparsa Zivari et al, Nonclassical mechanical states guided in a phononic waveguide, Nature physics (2022). DOI: 10.1038/s41567-022-01612-0
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