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Martin Nurizzo presents

 Controlled quantum dot array segmentation and complete two-electron spin state readout

Monday, January 16th 2023 at 10:00 am

Seminar room – Building A – CNRS

The defence will be in English.



Spin qubits in semiconductor quantum circuits have been identified as a compelling platform for large-scale quantum computing. Today an ongoing effort of the community is aiming at the scaling of such systems by filling larger and larger arrays. In this context, the development of tuning and readout protocols allowing to reduce the inherent complexity of such systems seems to be a necessity.

 In the first part of my thesis, I demonstrate array partitioning of a linear triple quantum dot defined in a AlGaAs/GaAs heterostructure via a highly tunable interdot tunnel coupling. This allows us to operate independently smaller sections of the array which reduces the number of available charge states for the system and therefore reduces its complexity during the tuning.

 The second part of my thesis is focused on reducing the hardware overhead necessary to extract information during the readout of the spin qubits. In semiconductor spin qubits, high-fidelity read-out is obtained through Pauli spin blockade in a double quantum dot with two electrons probed by a local electrometer. One electron is the qubit, the second is the ancilla and only one bit of information is extracted. To obtain the full two-bit information of the two-electron spin states, more quantum hardware is necessary (either dots, electrometers, or reservoirs). Based on an original protocol, I develop in this thesis a complete single-shot read-out procedure for two-electron spin states in a double quantum dot discriminating between S, T0, T+ and T-. It uses successively three distinct spin-to-charge conversion protocols interleaved with charge configuration measurements. The read-out procedure is tested on various initialized populations and implemented in more complex spin manipulation sequences to assess its validity.