Generation and manipulation of quantum sound

Project Information

Q-ECHOS

Grant agreement ID: 101001005

DOI

10.3030/101001005

Project closed

EC signature date 4 February 2021

Start date 1 March 2021

End date 28 February 2026

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 2 374 300,00

EU contribution

€ 2 374 300,00

Coordinated by

TECHNISCHE UNIVERSITEIT DELFT
Netherlands

Periodic Reporting for period 3 - Q-ECHOS (Generation and manipulation of quantum sound)

Reporting period: 2024-03-01 to 2025-08-31

Summary of the context and overall objectives of the project

Optical fibers and waveguides allow the transmission of quantum information encoded in optical photons. They have become an indispensable technology not only of quantum optics experiments and applications, but also for modern classical communication. Realizing the equivalent components for mechanical excitations has a similar potential to revolutionize the nascent field of quantum acoustics and phononics. Such low-loss phononic waveguides will not only allow to guide and transmit (quantum) information encoded in phonons over tens of centimeters on a chip, but will form the basis for full coherent control over traveling mechanical excitations.
Creating such a toolbox for quantum acoustics experiments will have a profound impact on quantum physics and allow for fundamentally new ways of interacting with quantum systems. Importantly, these acoustic waves are fundamentally different from the oscillation of single atoms or ions in traps, due to the associated large mass, their propagating character and the possibility to couple to a large variety of other quantum systems like quantum dots and superconducting qubits. Guiding single phonons is a crucial step towards realizing hybrid quantum devices and transfer quantum information over heterogeneous networks.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

In the first phase the project we have designed and realized the first waveguide for non-classical traveling mechanical excitations, which was published in Nature Physics. By fabricating the waveguide from thin film silicon we combine the waveguide with a source and detector for non-classical mechanical states, and we were able to verify the propagation of these quantum states in the waveguide. These acoustic waves at GHz frequencies are guided in a highly confined nanoscale geometries, with long lifetimes (up to several ms), in particular at low temperatures, enabling the faithful transport of quantum states over centimeter distances on a chip.
In the second phase of the project, we have demonstrated how such a waveguide can be used to distribute entangled states over a chip, which we then used to violate a Bell-type inequality, with the results published in Science Advances.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Compared to previous experiments, where phonons were not confined to a waveguide, our measurements increase the mechanical lifetime by more than 3 orders of magnitude, crucial for routing over the full chip scale. We further show how non-classical correlations emerging from phonons launched at different times are conserved throughout the propagation in our waveguide, by realizing a phononic FIFO quantum memory.

We are currently finalizing the demonstration of a phononic beamsplitter, which will allow us to realize advanced experiments such as a Hong-Ou-Mandel experiment and studying the decoherence of qubits through phonons. We will furthermore develop a deterministic phonon source based on a superconducting transmon qubit. Over the next period this should allow us to create phonon states with significantly enhanced rates in our waveguide.

Sketch of creating (1) a traveling single phonon inside a waveguide (2), which can then be detected