Extremely Coherent Mechanical Oscillators and circuit Cavity Electro-Optics

Project Information

ExCOM-cCEO

Grant agreement ID: 835329

DOI

10.3030/835329

Project closed

EC signature date 14 May 2019

Start date 1 October 2019

End date 30 June 2024

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 2 496 000,00

EU contribution

€ 2 496 000,00

Coordinated by

ECOLE POLYTECHNIQUE FEDERALE DE LAUSANNE
Switzerland

Periodic Reporting for period 3 - ExCOM-cCEO (Extremely Coherent Mechanical Oscillators and circuit Cavity Electro-Optics)

Reporting period: 2022-10-01 to 2024-06-30

Summary of the context and overall objectives of the project

Mechanical resonators are common in applications like accelerometers, motion sensors, and cell phone filters. A key factor in their sensitivity and performance is the quality factor (Q). Higher Q resonators are preferred for their improved sensitivity and noise isolation. This ERC project aims to develop resonators with extremely high Q factors, focusing on both amorphous and crystalline materials. Crystalline materials, in particular, offer highly coherent oscillators at low temperatures, surpassing current mechanical oscillators. We will also explore superconducting electromechanical systems, developing methods to couple superconducting qubits with ultracoherent mechanical resonators on a chip. This approach seeks to enhance superconducting computing by providing coherent quantum memory with longer coherence times than current qubits. To address challenges in transmitting quantum information over long distances, we will create technologies to convert microwave signals to the optical domain, enabling transmission via optical fibers and overcoming heat load issues with large numbers of qubits. Our project will advance mechanical-based sensing and establish new methods for converting microwave and optical signals.

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 project’s first and second objectives, we made significant strides with ultracoherent hierarchical and polygon resonators, as well as strained silicon nanomechanics. We introduced an innovative method for creating low-dissipation mechanical resonators by leveraging hierarchical string branching, achieving a quality factor of 780 million at 107 kHz at room temperature. Polygon resonators reached a record quality factor of 3.6 billion at room temperature in more compact devices. We also achieved a 13 billion quality factor for 1 MHz resonators at 6 K using strained silicon on insulator (sSOI) and developed density-modulated membranes and an ultralow noise optical cavity, demonstrating optomechanical squeezing of light at room temperature.

To advance superconducting electromechanical devices, we developed a nanofabrication process for ultracoherent resonators for superconducting circuits. We installed a new cryogenic dilution fridge funded by the ERC project, achieving twice the quality factors of our previous system. This fridge enabled us to record a mechanical quality factor of 40 million and perform quantum ground state cooling of mechanical motion, measuring 0.07 quanta occupation. We also established a time-domain setup for pulse sequential measurements, showing 3 dB squeezing of mechanical motion below vacuum. Our fabrication process led to multimode electromechanical circuits demonstrating topological lattices, showcasing quantum collective phenomena.

We progressed in studying dynamical backaction in circuit cavity electro-optics by establishing integrated nonlinear photonic platforms for strong microwave-optical interactions. These included direct etching of lithium niobate (LN) and lithium tantalate, and integrating LN on silicon nitride circuits. We demonstrated various photonic devices, including low-loss microresonators and frequency combs. We developed piezo-optomechanical transducers based on sub-wavelength modes in gallium phosphide and piezoelectrically coupled resonances (highlighted by an EPFL press release (1)). We also developed a cryogenic electro-optical interconnect to optically read out superconducting circuits, using a commercial phase modulator for microwave-to-light transduction at 800 mK, enabling long-range transmission via optical fibers.


(1) A novel on-chip microwave-optical transducer. https://actu.epfl.ch/news/a-novel-on-chip-microwave-optical-transducer-2/

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 newly developed density-modulated membranes and ultralow noise optical cavity enabled us to demonstrate light squeezing at room temperature. Our next goal is to improve these membranes' quality factor to achieve ground state cooling of mechanical oscillators at room temperature, addressing a long-standing challenge. Room temperature operation will simplify experiments and eliminate the need for cryogenic techniques.

Our advancements in electro-optomechanics have significantly extended coherence times, allowing us to study quantum regime dynamics. We are developing hybrid systems coupling superconducting qubits with mechanical resonators, aiming for long-lived quantum memory. Our precise control over mechanical frequencies and system reproducibility enables exploration of quantum collective phenomena. We are also investigating new crystalline superconducting materials to further enhance mechanical oscillator quality factors.

Our work on electro-optic dynamical backaction has led to novel microwave-optical transducers, potentially transforming quantum computing. Current superconducting qubits are limited by dilution refrigerator technology, and microwave-domain quantum information is not feasible at room temperature. We aim to process quantum information in the microwave domain and transmit it using optical qubits, utilizing new microwave-optical conversion platforms. Coupling superconducting qubits with other quantum systems could advance quantum computing. Our new photonic platforms have already impacted the industry, exemplified by the EPFL spin-off LUXTELLIGENCE SA, a lithium niobate (LN) foundry based on our fabrication process. These technologies are expected to benefit telecommunication and photonic industries by providing energy-efficient electro-optic modulators.

All data and experimental details from our publications are available on public repositories like ZENODO (https://zenodo.org/) and arXiv (https://arxiv.org/). Our group has also developed a platform for sharing nanofabrication processes (https://nanofab-net.org/) which reduces time and resources spent in nanofabrication and promotes Open Science, enhancing transparency and research reliability.

Ultra-high Q electro-mechanics