Carbon nanotube based nanomechanical qubit

Project Information

CNTQUBIT

Grant agreement ID: 101023289

DOI

10.3030/101023289

Project closed

EC signature date 5 March 2021

Start date 1 April 2021

End date 31 March 2023

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 160 932,48

EU contribution

€ 160 932,48

Coordinated by

FUNDACIO INSTITUT DE CIENCIES FOTONIQUES
Spain

Periodic Reporting for period 1 - CNTQUBIT (Carbon nanotube based nanomechanical qubit)

Reporting period: 2021-04-01 to 2023-03-31

Summary of the context and overall objectives of the project

Many modern challenges such as climate change and food security are difficult to address using classical computing. Quantum computers are expected to fare much better, because their fundamental computing unit, the quantum bit (qubit) can utilize quantum properties such as entanglement. These qubits are in practice realized on a specific hardware platform, but so far, no particular architecture has demonstrated superiority.

This project sought to demonstrate a fundamentally new type of platform to host such qubits. The qubit is realized with a carbon nanotube (CNT) whose mechanical vibrations are coupled to an embedded and trapped electron. The first objective was to demonstrate the interplay between the vibrations and the electron, whilst the second was to utilize this coupling for the formation of a qubit.

The image shows a scanning electron micrograph image of our platform. The carbon nanotube is indicated by the red arrows are grows from catalyst nanoparticles in the blue regions. The electron is confined along the suspended nanotube in the small region indicated by the dashed yellow rectangle by applying voltages to the electrodes highlighted in red.

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

Work performed

o Single quantum dot (SQD) lithographic designs. 12 wafers.
o Double quantum dot (DQD) lithographic designs. 56 wafers.
o Superconducting microwave cavity designs. 27 wafers.
o Carbon nanotubes devices in SQD and DQD architectures.
Catalyst deposition, CVD, vacuum probe station measurements
Cryogenic measurements in dilution refrigerator
o Communication of work and results at 4 conferences

Main results

o Ultra-strong coupling between SQD and mechanical vibrations (published)
o Robust lithographic architecture for making DQDs (published)
o High quality factor superconducting resonators in CVD compatible material

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)

Carbon nanotubes have never been reliably grown in-situ over sufficient gates to form complex architectures such as DQDs. We developed such a process which is now the state-of-the-art. Similarly, state-of-the-art DQDs are often integrated with superconducting circuits, but these circuits and their small lithographic dimensions were not compatible with the CVD conditions necessary to grown CNTs in-situ. We developed a lithographic process for NbN that can be integrated with the DQDs whilst remaining superconducting after CVD. This progress may have implications for various qubit start-ups using carbon nanotubes, such as C12 Quantum Electronics, or emerging technologies wishing to integrate lithographically defined graphene with superconducting circuits.


Single QDs were also ultra-strongly coupled to mechanical vibrations of the carbon nanotube with a coupling rate 16.5 times larger than the mechanical frequency. This is far beyond the state-of-the-art for electromechanical resonators. The previous state-of-the-art was 2.7. Additionally, we observed non-linear thermal vibrations as a result of this ultrastrong coupling. This progress may

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