Periodic Reporting for period 3 - QBusSi (Optomechanical quantum bus for spins in silicon)
Reporting period: 2023-03-01 to 2024-08-31
By many accounts, quantum computing will be one of the defining technologies of this century. A general-purpose quantum computer could significantly speed-up various calculation intensive tasks ranging from drug research to optimization of logistics routes with immediate societal benefits. Many different materials are studied as the basis on which a quantum computer could be build. In this project, we will advance the use of silicon, the material that is already ubiquitous around us, as a quantum platform. As silicon has already been the material underpinning the modern information technology revolution, using it would be of advantageous to the diffusion of quantum technologies as they could then leverage the existing infrastructure of silicon electronics and photonics. The ultimate long-term goal of the project is enabling a not-too-distant future where silicon chips encompassing quantum enabled sensors and/or quantum computing processors are widely available and only require push-of-a-button coolers and laser light to operate.
Specifically, the project will advance a novel emerging physical implementation of qubits: donor spin states in silicon. These states are now known to be excellent qubits with some of the longest single qubit coherence times demonstrated in solid state. This is a significant advantage for both quantum sensing and quantum information applications. However, at the moment the application potential of silicon donor qubits is hindered by two related obstacles: current readout techniques require nanoelectric connections, below 1 K temperatures and high magnetic fields, and - most importantly - there are no scalable methods to couple multiple qubits.
This project will realize an optomechanical quantum bus for spins in silicon in order to enable optical and mechanical coupling and readout mechanisms for the donor spins and hence overcome all these obstacles. The created quantum bus will not only allow integrating the spin qubits with existing silicon photonics and nano-electro-mechanical (NEMS) platforms for integrated quantum circuits and optically readable practical quantum sensors but will also provide a solid-state on-chip testbed for creating and studying macroscopic quantum states.
Specifically, the project will advance a novel emerging physical implementation of qubits: donor spin states in silicon. These states are now known to be excellent qubits with some of the longest single qubit coherence times demonstrated in solid state. This is a significant advantage for both quantum sensing and quantum information applications. However, at the moment the application potential of silicon donor qubits is hindered by two related obstacles: current readout techniques require nanoelectric connections, below 1 K temperatures and high magnetic fields, and - most importantly - there are no scalable methods to couple multiple qubits.
This project will realize an optomechanical quantum bus for spins in silicon in order to enable optical and mechanical coupling and readout mechanisms for the donor spins and hence overcome all these obstacles. The created quantum bus will not only allow integrating the spin qubits with existing silicon photonics and nano-electro-mechanical (NEMS) platforms for integrated quantum circuits and optically readable practical quantum sensors but will also provide a solid-state on-chip testbed for creating and studying macroscopic quantum states.
At this point of the project, we have now designed and fabricated devices that combine the implanted ions and optomechanical devices and are currently working on characterising the spin - mechanical resonator coupling. For a complete functionality of the hybrid system it would beneficial to have also a second readout in addition to the optomechanical device, and for this reason we are also working on another readout mechanism based on donor bound exciton states. This work lead us to some interesting physics about how hole states in silicon react to strain. Finally, as the ultimate device will also require us to have a quantum level control over the mechanical resonator, we are simultaneously working on measurement based feedback of optomechanical systems. This work in turn lead us to realise a novel way to achieve the feedback mechanism.
By the end of the project we expect to have a quantum device where donor spins in silicon are coupled to silicon NEMS devices which provide both the spin-spin coupling for the nearest neighbors and a transducing element between the spins and optical telecom range photons that can then be used for long-range interactions. This will be the crucial building blocks to realize a full size silicon quantum computer.