Long distance qubit-qubit coupling in silicon quantum dots

Lead Research Organisation: University College London
Department Name: London Centre for Nanotechnology


Abstract: I study the interaction between quantum mechanical spins controllably trapped in small regions known as quantum dots at the interfaces of a semiconductor, such as silicon, and and an insulator. Even though the electric field of an electron is spherical, electrons have orientation, the spin. Spins can encode information, which can be controlled with the help of electric and magnetic fields. Electron spins in quantum dots can be studied in cold environments provided by so-called dilution refrigerators, which cool them and their immediate environment down very close to absolute zero. Such cold temperatures are required to differentiate the faint signals transmitted by these tiny particles from the ones caused by inevitably noisy environment.

To fully process the information contained in spins, they need to interact with one another in a well-defined manner. I study an interaction which can be seen as an interplay of two facts. First, two electrons repel each other due to both having a charge with the same signature. Second, two electrons with exactly the same energy and orientation cannot occupy exactly the same physical space. In systems where two nearby electrons are trapped, they repeatedly swap their spin orientations with one another. This effect is known as the exchange interaction.

It turns out that the outer electrons in a system of three or more quantum dot electrons can also interact via spin exchange. We aim to apply this effect to demonstrate qubit-qubit interactions over distances that are long compared to quantum dot sizes. In particular, we aim to study the controllability and quality of the resulting two-qubit gates. If sufficiently strong and controllable, such and interaction would be a helpful step towards realising scalable qubit processors.


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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/P510270/1 31/03/2016 30/08/2022
1937062 Studentship EP/P510270/1 24/09/2017 30/03/2022 Sofia Marjatta Patomäki
Description Simulation/theoretical results:
-estimates for parameters of optimized qubit-qubit couplers in so-called planar MOS and SOI nanowire silicon spin qubit platforms (the specialist terms refer to specific industry compatible fabrication styles)
-new quantum computing architecture ideas (currently being written up as a publication, and some patented)
-new device designs, to be fabricated externally (which are in the progress of being written up as a publication, and some patented)

Experimental results:
-basic characterization results for few quantum dot systems fabricated in the planar MOS style mentioned above, which support the above mentioned external foundry doing the fabrication
Exploitation Route -patents
-simulation programs
-other minor progress, such as custom PCBs or other small equipment, etc.
Sectors Electronics,Other

Description imec 
Organisation Interuniversity Micro-Electronics Centre
Country Belgium 
Sector Academic/University 
PI Contribution -measuring and designing quantum dot devices
Collaborator Contribution -fabrication of quantum dot devices
Impact -basic characterization results that are guiding future designs
Start Year 2017
Description -hardware (i.e. device) patent related to realizing surface code (quantum error correction method for quantum computing) in realistic near term silicon spin qubit platform 
IP Reference 1903884.3 
Protection Patent application published
Year Protection Granted 2020
Licensed No
Impact -so far only academic impact
Description -software, i.e. method patent related to realizing surface code architecture in a realistic scenario with silicon spin qubits 
IP Reference  
Protection Patent application published
Year Protection Granted 2020
Licensed No
Impact -so far purely academic