Initialization and Readout of Nuclear Spins via a Negatively Charged Silicon-Vacancy Center in Diamond

Abstract

In this work, we demonstrate initialization and readout of nuclear spins via a negatively charged silicon-vacancy (SiV) electron spin qubit. Under Hartmann-Hahn conditions the electron spin polarization is coherently transferred to the nuclear spin. The readout of the nuclear polarization is observed via the fluorescence of the SiV. We also show that the coherence time of the nuclear spin (6 ms) is limited by the electron spin-lattice relaxation due to the hyperfine coupling to the electron spin. This work paves the way towards realization of building blocks of quantum hardware with an efficient spin-photon interface based on the SiV color center coupled to a long lasting nuclear memory.Recent advances with color centers in diamond based on IV-group elements [1-4] hold promise to provide an efficient interface between photons and spin qubits. These color centers possess a high Debye-Waller factor (larger than 0.5) [5,6], which implies a high flux of coherent photons, and furthermore an exceptional spectral stability owing to the inversion symmetry of the defects [7,8]. Both of these properties are crucial to realize long distant entanglement based on light-matter interface [9][10][11] which forms an essential building block for scalable quantum processors and quantum repeaters. However, these color centers are not free of constraints. A main drawback is the limited coherence time of the electron spin which is induced by a fast phonon mediated relaxation process between the orbital branches of the ground state [12]. Different attempts to overcome this problem were recently demonstrated, including the application of high strain [13] or freezing of the specimen to millikelvin temperatures [14]. Of these two methods, the former leads to symmetry distortion that affects the optical properties, while the latter requires dilution refrigerators, which are expensive and offer only limited cooling capability. Another route to beat this limitation is to use a defect of this family only as a spin-photon interface and readout gate, while storing the information on a long living nuclear memory. However, to realize such a hybrid approach several problems have to be tackled. Among them are the initialization of the nuclear memory and its readout. The simple polarization technique utilizing level anticrossing and optical pumping commonly used for NV center coupled to 13 C or ST1 centers [15,16] is not applicable to the systems of SiV family. In this letter, we report deterministic polarization of a small nuclear spin ensemble via a dynamic nuclear polar- * petr.siyushev@uni-ulm.de ization protocol. By measuring the Larmor precession in different magnetic fields we identify these nuclei as 13 C. From this ensemble, we choose one nuclear spin with coupling strength in the order of few hundred kHz. This 13 C spin is used to demonstrate nuclear magnetic resonance and Rabi oscillations via nuclear spin polarization readout protocol. For the experiment, a 111 -oriented diamond sample containing ingrown SiV center was chosen and placed ...

Building Blocks for Quantum Network Based on Group‐IV Split‐Vacancy Centers in Diamond

“…Since the identification of spin dephasing mechanism in split‐vacancy centers, enormous progress has been made in the fields of coherent control of the associated quantum states and in device engineering of photonic nanostructure. Suppression of spin–phonon interaction has been achieved by cooling the system down to sub‐Kelvin temperature or employing strain engineering, both of which open the door for accessing nuclear ancilla memory via electron qubit . Isotopically pure environment suppresses most of the magnetic noise stemming from the inevitable fluctuations of nuclear spins and boosts the spin coherence time up to millisecond regime with the help of dynamical decoupling protocol .…”

“…Although understanding of the residual noise bath and its effect on spin dynamics is critical for further improvement of qubit performance, current 13 ms long coherence is sufficient for transmitting quantum states between two quantum nodes separated by ≈100 km . Other tools like robust dynamical decoupling, deterministic charge‐state control, and nuclear spin access via double‐resonance protocol offer appealing opportunities for longer quantum memory lifetime, which requires further investigations.…”

“…Later on, qubit formed by a single 13 C nucleus in the vicinity of an NV − center, or next to an ST1 center is also demonstrated. Recently, Metsch et al . show that SiV − center can also be used as a sensitive probe to initialize and read out the nuclear spin of a nearby 13 C atom that dynamically couples to the SiV − electron via Hartmann–Hahn double resonance .…”

Making Diamond Qubits Talk to Light

“…Finally, this scheme relies on a second order splitting of individual 13 C resonances to resolve individual ones; residual coupling to additional 13 C limits the fidelity for a pulse sequence of given total length. Direct RF control [24] would be a simple way to make a fast and high-fidelity CNOT gate since it would require a single RF π pulse on a nuclear spin transition [66]. Furthermore, since the nuclear spin transition frequencies depend on the hyperfine coupling to leading order, these pulses could have higher 13 C selectivity and potentially shorter gate duration.…”

“…Recent work has established the silicon-vacancy colorcenter in diamond (SiV) as a promising candidate for quantum networking applications [19][20][21][22][23][24]. The SiV is an optically active point defect in the diamond lattice [25,26].…”