PhD researcher on decoherence dynamics in spin-qubits

Leuven - PhD
Meer dan twee weken geleden

The continued demand for increasing computing power has led to miniaturization of conventional CMOS technologies over the past decades. Eventually, the scaling of the CMOS technology nodes, may reach an end, as fundamental physical barriers are expected to be soon reached. An increasingly large effort is therefore placed on researching novel devices and alternative computing paradigms that can overcome the computational limits as projected today. In this context, quantum computing is seen as a rapidly emerging research field that has the potential to bring to practice technologies exploiting massive parallelism, enabling computational power way beyond the contemporary realm.
The spin is seen as one of the most promising carrier of quantum information, due to its relatively low coupling to the environment, which would enable quantum computation to evolve in time.  Localized electron spins in semiconductor quantum dots provide an attractive path to pursue, due to the remarkable background provided by a mature semiconductor industry that can sustain the huge development effort needed, and translate the academic research into technological platforms for future computational architectures.

Realization of any practical quantum computing system needs to account for a set of requirements, among which being able to scale-up massively the number of qubits, to couple them, and to reach operating fidelities that exceed the thresholds imposed by fault-tolerance. From this angle, one limiting factor is the qubit decoherence. This is caused by uncontrolled interactions between the qubit and its environment and is typically expressed by two characteristic times: the excited state lifetime (T1), i.e. the time it takes an excited state |1> to decay/relax to the ground state |0>, by exchanging energy with the environment, and the dephasing time (T2), i.e. the time it takes for the phase of a qubit state to randomize. This latter time is eventually the most limiting parameter impacting the qubit coherence. Next to an extensive experimental effort to quantify the scale of these times and the material, process or device parameters affecting or controlling it, it is of major importance to develop models able to support the understanding of decoherence mechanisms, of the main noise sources, and to point out directions for improvement. These models need to take into account specific qubit implementations, as well as the local disorder associated with imperfections in materials and material interfaces.

Your role will be to develop models for the dynamics of the qubit state decoherence, to translate them down to methods to experimentally test and validate them, to feedback to process and device design for improving the overall qubit performance. You will work closely with an internal team of process, device and system experts, to define, develop, test and validate models that will improve device understanding and support further device innovation and engineering in view of realization of scalable spin-qubit architectures. You will have the opportunity to collaborate with top-notch research groups, through imec’s network of academics and joint research programs. You need to have a very good knowledge of relevant physics and of recent developments in spin-qubit research areas, a good overview of CMOS technologies, be willing to pursue experimental work in complement of theoretical developments, be skilled in programming and fluent in English.

References: Veldhorst et al, Nature 526: 410, 2015; Watson et al, Nature 555: 633, 2018; Russ & Burkard, J Phys Cond Matt 29: 393001; Bechtold et al, Nature Phys. 11:1005, 2015; Fischer et al, Solid State Communications 149(35-36):1443-1450; Hung et al, Phys Rev B 90:045308, 2014; Wu & Das Sarma, Phys. Rev. B 96: 165301, 2017.

Type of work: 70% modeling/simulation, 20% experimental, 10% literature.

Supervisor: Iuliana Radu

Daily advisor: Bogdan Govoreanu

The reference code for this PhD position is STS1804-02. Mention this reference code on your application form.


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