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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - NAMESTRANSIS (Nanomechanical spin-to-photon transduction in silicon)

Teaser

Summary

Silicon has been the material underpinning the modern information technology (IT) revolution. It has recently been discovered that it could very well be the most important material for the upcoming quantum IT age as well. Using the spin of an electron trapped in the binding potential of a phosphorous donor as a qubit, the funded fellow and co-workers at UNSW Australia in 2014 demonstrated the longest quantum coherence times ever seen in solid state (apart from nuclear spin ensembles). Combined with also demonstrated high-fidelity quantum coherent control and the possibility of leveraging the huge manufacturing capabilities of the current semiconductor industry, silicon is now seen as one of the most promising materials for building a universal quantum computer.

A crucial challenge ahead for donor qubits is the realization of suitable coupling and readout mechanisms. The natural way to couple donor spin qubits via the exchange interaction will require placement of the donors with an atomic accuracy that is not achievable in current fabrication processes. Current readout techniques rely on energy dependent tunnelling to an electron reservoir, for which high magnetic fields and millikelvin electron temperatures are needed. A coupling principle that alleviates these limiting requirements would provide a defining advantage, leveraging the application potential of silicon for quantum applications.

In this project our objectives were to study a new readout and coupling mechanism for the donor qubits, based on nano-optomechanical structures. For this purpose optomechanical photonic crystal structures were developed further to maximize the photon-phonon coupling strengths and to demonstrate measurement and control of the mechanical degree of freedom close to the quantum level using pulsed measurements. Then spins were embedded to the structures in order to make proof-of-principle measurements on the spin-mechanics-light coupling.

Work performed

In this project our objectives were to study a new readout and coupling mechanism for the donor qubits, based on nano-optomechanical structures. Nanomechanical resonators are envisioned to work as transducers between silicon donor spins and optical photons. For this purpose high-quality nano-optomechanical systems in silicon are required that allow on the one hand coupling spins to motion, and on the other hand strong interactions with cavity photons for the efficient readout of motion with light. The optomechanical photonic crystal structures studied by the host group were used as a starting point for such systems. They were further developed to maximize photon-phonon coupling strengths, to study their cryogenic properties, and to demonstrate measurement and control of the mechanical degree of freedom close to the quantum level. In these efforts, the strong photon-phonon coupling of the optimised optomechanical nanocavities revealed new non-linear phenomena. The devices were presented, together with studies of optomechanical measurement and optical forces in this regime of nonlinear optomechanics, in a publication in the journal Nature Communications in 2017. Phosphorous donor atoms were embedded to the structures to study ways to couple their spins to mechanical motion and make proof-of-principle measurements on the spin-mechanics-light coupling (WP1). In the context of WP2, we studied fast, back-action evading optical measurements of motion as means to sensitively transduce mechanical excitations to light signals.

The scientific results have been published in journal publications (1 Nature Communications, 1 under preparation, expected submission May 2018). The developed principles and systems impact the fields of quantum technology, showing new routes to interface solid-state spin systems to optical photons, and quantum measurement, proving a new platform for studies of quantum backaction and nonclassical states in macroscopic mechanical systems. The results of the project have been disseminated in numerous conferences. The funded fellow has given an oral presentation at following international conferences Physics@Velhoven 2016 (Netherlands), Metaâ€™16 (Spain), Quantum Interfaces with Nano-optic-electro-mechanical devices 2016 (Italy), APS March Meeting 2017 (US), APS March Meeting 2018 (US), and Gordon Research Seminar on Mechanical Systems in the Quantum Regime 2018 (US). In addition, he presented posters at Gordon Research Conference on Mechanical System in the Quantum Regime both in 2016 (US) and in 2018 (US) and at Physics@Veldhoven both in 2017 (Netherlands) and in 2018 (Netherlands).

Final results

Optical readout of spin states in silicon and creation of nonâ€classical mechanical states are both longâ€standing goals of the research community and the research performed in this project contributed significantly into these research directions. It showed how nanophotonic optomechanical systems can be used for strong measurements of nanomechanical displacement, and as transducers that form an interface between light, which is the best carrier of quantum information over long distances, and other quantum systems. The project opened up two new research avenues in the host group (pulsed optomechanics and spin-optomechanics) and equipped the funded fellow with unique expertise to continue pursuing quantum technologies in silicon with hybrid systems.

As expected, the grant allowed the funded fellow to re-integrate himself to the European research community and positioned him well for a research position in Europe, culminating in securing a tenure-track position. The project allowed the applicant to gain crucial expertise in nano-optomechanics and nanophotonics in the excellent scientific environment of the host institute, and gave him a unique background in both spin qubits and nanophotonics. Also, it gave him experience in the managing aspects of supervising a small team of people. At the same time, the host group benefited from the low temperature and quantum physics background of the applicant in going towards cryogenic experiments approaching the quantum regime.

The project also involved the development of several new measurement methods and setups. Most importantly the development and operation of a lowâ€temperature lowâ€vibration homodyne interferometric measurement setup. This kind of measurement setup was new both for the host group and the funded fellow. This new scientific tool was successfully built and deployed and is expected to be very beneficial for both parties in the future, as well as for other researchers in the field.