Quantum Cavity Electro- and Opto-Mechanics

Project Information

Q-CEOM

Grant agreement ID: 638765

DOI

10.3030/638765

Project closed

EC signature date 17 March 2015

Start date 1 July 2015

End date 30 June 2021

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 495 073,00

EU contribution

€ 1 495 073,00

Coordinated by

KOBENHAVNS UNIVERSITET
Denmark

Periodic Reporting for period 4 - Q-CEOM (Quantum Cavity Electro- and Opto-Mechanics)

Reporting period: 2020-01-01 to 2021-06-30

Summary of the context and overall objectives of the project

Next-generation electronic and optical systems can be operated in a quantum regime, in which effects such as quantum correlations and entanglement are employed to realise higher measurement precision and novel information processing schemes. Such capabilities can be further extended if subsystems can be linked in a coherent way, that is, without perturbing the quantum mechanical properties of the electronic and optical signals. One application is a quantum "modem", that translates electronic quantum signals into optical signals that can be propagated through optical fibre. This would enable the implementation of quantum sensor and computing networks across laboratories, cities or even continents.

Realising such links necessitates physical systems that are coherent, and couple to optical and electronic signals alike. In this project, we develop nanomechanical resonators coupled to microwaves and light through capacitive and radiation pressure forces. They are designed to be highly coherent in spite of the inevitable coupling to a thermal environment. In this manner, they will be able to transfer signals, and mediate correlations between different domains of the electromagnetic spectrum as required.

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

Addressing the first challenge we have realized nanomechanical resonators with unprecedented mechanical coherence. They are based on a novel method called soft-clamping. It relies on the combination of phononic crystals with strain-based dissipation dilution. This groundbreaking invention, made within this project, relaxes requirements for quantum-coherent opto- and electro-mechanical coupling. It may even lead to new applications in force-sensing, nano-imaging, and gravitational astronomy.

By coupling soft-clamped membrane resonators to an optical field we could realize optical measurement of motion close to the standard quantum limit (SQL). Based on such precise measurements, we could, for the first time, control the motional quantum state of the membrane using quantum feedback, and cool it to its ground state. Exploiting quantum correlations born in the measurement process, we could also beat the SQL for both position and force measurements.

Furthermore, were could generate quantum correlations between two laser fields of different wavelength, mediated by their interaction with a single membrane resonator. We could show that the light fields emerging from the interaction are indeed entangled. This hallmark of quantum physics signals the potential for mechanically-mediated interactions for quantum information processing.

Addressing the second challenge, we have realized electromechanical systems with superconducting microwave resonators capacitively coupled to soft-clamped, metallized membranes. The system’s high coherence enables a strong quantum cooperativity, and thereby ground state cooling of the mechanical system via microwave backaction.

Finally, we have performed theoretical studies to determine relevant figures of merit for quantum transducers. An important outcome is a detailed analysis of the importance of transfer efficiency and added noise, depending on the task of the transducer. Further work has made the project’s topic accessible to a broader audience, by taking a microwave engineering perspective, as well as giving a broader overview of nano-electro-optomechanical systems.

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)

The project has significantly advanced the state of the art in the field at several fronts, a selection of which is listed in the following.

First and foremost stand the unprecedented Q-factors in excess of 1 billion at 1 Megahertz oscillation frequency, which were first achieved within this project. This constitutes an advance of several orders of magnitude over earlier results.

Secondly, measurement-based quantum control of mechanical motion had been attempted for more than 20 years, unsuccessfully, with a wide variety of approaches, including trapped atoms, optomechanics, and gravity wave detectors. It was first achieved within this project.

Third, the Standard Quantum Limit (SQL) had been elusive in measurements of mechanical motion, for more than 30 years since it had been first described. It was reached, and indeed even broken, for the first time in this project.

Finally, at milliKelvin temperatures, the electromechanical systems developed in this project have unprecedentedly low heating rates of only a few phonons per second.

Feedback cooling to the quantum ground state: shown is the mechanical occupancy for different quantu

Quadrature noise of two optical modes A,B showing Einstein-Podolsky-Rosen entanglement. Shown are hi

Vibration amplitude of extremely coherent (Q>10^9) modes in a soft-clamped membrane resonator.

Quantum measurement of displacement around the effective mechanical frequency, for different quantum