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Developing the spin qubit of the tin-vacancy center in diamond for quantum networks


Type

Thesis

Change log

Authors

Debroux, Romain 

Abstract

Quantum technologies working towards quantum computation and quantum communication have made tremendous progress over the past few years, highlighted by the 2019 "quantum supremacy" achievement demonstrating that quantum computers can realize calculations intractable to classical computers [5]. However, these technologies are currently struggling with scaling beyond proof-of-concept demonstrations. A quantum network would provide the solution to this scalability challenge, by connecting individual quantum computers into a single more powerful quantum computer, or allowing communication between multiple remote parties [6, 7]. However, building a quantum network requires developing a system with excellent spin and photonic properties [8]. To date, no system has demonstrated excellence in both of these regards simultaneously. At a high level, this thesis develops the spin properties of the tin-vacancy (SnV) center in diamond, a system for which the excellence of the photonic properties have already been demonstrated. Specifically, this thesis presents the (1) first measurements of key properties of the SnV spin qubit such as its lifetime and coherence time, (2) the first demonstration of quantum control over the SnV spin qubit, and (3) the utilization of quantum control to prolong the SnV spin qubit coherence time by three orders of magnitude at a readily attainable temperature of 1.7 K. At a more granular level, the first set of measurements ("Probing the SnV spin qubit") uses the the direct microwave drive technique (DMDT) to measure the SnV spin qubit inhomogeneous coherence time T2* = 540(40) ns. This coherence time is found to be limited by the nuclear spin bath and in theory could be prolonged to the spin lifetime measured to be T1 = 10(2) ms. Ultimately, the strong spin-orbit effect characteristic of the SnV center suppresses the effectiveness of the DMDT and leaves quantum controlout of reach. In the second set of measurements ("Controlling the SnV spin qubit"), the all-optical drive technique (AODT), which intrinsically circumvents the issues posed by the large spin-orbit effect, is utilized to achieve quantum control of the SnV spin qubit with a control rate of 19.1(1) MHz and a fidelity of Fπ/2 = 90.9(7)%. In the third set of measurements ("Shielding the SnV spin qubit"), quantum control is leveraged to implement Ramsey interferometry revealing an inhomogenous coherence time T2* = 1.3(3) μs and dynamical decoupling protocols prolonging the coherence time to T2 = 300(80) μs at 1.7 K. These results establish that the SnV center possesses the desired combination of spin and photonic properties necessary to be the building block for the quantum networks promising to unlock large scale quantum computation and communication technologies.

Description

Date

2022-11-20

Advisors

Atature, Mete

Keywords

quantum network, diamond, SnV, tin-vacancy center, Rabi oscillations, Ramsey interferometry, Dynamical decoupling, CPMG

Qualification

Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge

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