Transform-limited photons from a coherent tin-vacancy spin in diamond

Solid-state quantum emitters that couple coherent optical transitions to long-lived spin qubits are essential for quantum networks. Here we report on the spin and optical properties of individual tin-vacancy (SnV) centers in diamond nanostructures. Through cryogenic magneto-optical and spin spectroscopy, we verify the inversion-symmetric electronic structure of the SnV, identify spin-conserving and spin-flipping transitions, characterize transition linewidths, measure electron spin lifetimes and evaluate the spin dephasing time. We find that the optical transitions are consistent with the radiative lifetime limit even in nanofabricated structures. The spin lifetime is phononlimited with an exponential temperature scaling leading to $T_1$ $>$ 10 ms, and the coherence time, $T_2$ reaches the nuclear spin-bath limit upon cooling to 2.9 K. These spin properties exceed those of other inversion-symmetric color centers for which similar values require millikelvin temperatures. With a combination of coherent optical transitions and long spin coherence without dilution refrigeration, the SnV is a promising candidate for feasable and scalable quantum networking applications

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

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

Quantum Control of the Tin-Vacancy Spin Qubit in Diamond

Group-IV color centers in diamond are a promising light-matter interface for quantum networking devices. The negatively charged tin-vacancy center (SnV) is particularly interesting, as its large spin-orbit coupling offers strong protection against phonon dephasing and robust cyclicity of its optical transitions toward spin-photon-entanglement schemes. Here, we demonstrate multiaxis coherent control of the SnV spin qubit via an all-optical stimulated Raman drive between the ground and excited states. We use coherent population trapping and optically driven electronic spin resonance to confirm coherent access to the qubit at 1.7 K and obtain spin Rabi oscillations at a rate of ω/2π=19.0(1) MHz. All-optical Ramsey interferometry reveals a spin dephasing time of T2∗=1.3(3) μs, and four-pulse dynamical decoupling already extends the spin-coherence time to T2=0.30(8) ms. Combined with transform-limited photons and integration into photonic nanostructures, our results make the SnV a competitive spin-photon building block for quantum networks.QID/Hanson La

Quantum Control of the Tin-Vacancy Spin Qubit in Diamond

Group-IV colour centres in diamond are a promising light-matter interface for quantum networking devices. We demonstrate multiaxis coherent control of the SnV spin-qubit via an all-optical stimulated Raman drive between the ground and excited states.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.QID/Hanson La