Locking of electron spin coherence above 20 ms in natural silicon carbide

Abstract

We demonstrate that silicon carbide (SiC) with natural isotope abundance can preserve a coherent spin superposition in silicon vacancies over unexpectedly long time approaching 0.1 seconds. The spin-locked subspace with drastically reduced decoherence rate is attained through the suppression of heteronuclear spin cross-talking by applying a moderate magnetic field in combination with dynamic decoupling from the nuclear spin baths. We identify several phonon-assisted mechanisms of spin-lattice relaxation, ultimately limiting quantum coherence, and find that it can be extremely long at cryogenic temperature, equal or even longer than 8 seconds. Our approach may be extended to other polyatomic compounds and open a path towards improved qubit memory for wafer-scale quantum techmologies.PACS numbers: 76.30. Mi, 42.50.Dv, 76.70.Hb Introduction -Long electron quantum coherence in solid-state systems is the ultimate prerequisite for new technologies based on quantum phenomena [1,2]. Particularly, the sensitivity of quantum sensors scales with the electron spin coherence time T 2 [3,4]. One of the common sources of decoherence is the interaction with fluctuating nuclear spins, and the usual way to prolong spin coherence is to perform isotope purification of the crystal. Indeed, the longest electron T 2 times of about 1 s and 0.6 s have been reported for spin-free silicon 28 Si and diamond 12 C crystals, respectively [5,6]. However, isotope purification is a technologically demanding procedure, which is not always possible. Therefore, one of the key challenges in quantum information science is to achieve long-lived spin coherence in natural materials.To address this goal, we combine two approaches. First, we exploit the suppression of mutual spin flip-flop processes between different types of nuclei in binary compounds, which occur in strong enough magnetic fields according to the theoretical simulations of Ref. [7]. Second, we use a periodic train of radiofrequency (RF) pulses to refocus spin coherence and decouple electron spins from inhomogeneous environment, similar to that applied for color centers [6] and quantum dots (QDs) [8].In recent years, SiC is attracting continuously growing interest as a technologically perspective platform for quantum spintronics [9][10][11][12][13][14][15][16][17] with the ability for single spin engineering and control [18][19][20][21]. The longest T 2 in SiC reported to date is 1 ms at cryogenic temperature [19]. We observe that in a finite magnetic field, a coherent spin superposition can be locked over longer time, which continuously increases up to about 75 ms with the number of decoupling pulses. The absence of saturation indicates that the longest possible spin locking time T

Electron spin coherence of silicon vacancies in proton-irradiated 4 H -SiC

“…When the overall trend is viewed, the coherence times in both samples appear to be enhanced in the region from 60-160 K. This behavior is remarkable, as the dominant spin dephasing mechanisms usually result in a continuous decrease of spin lifetime with temperature. For example, in both experimental and theoretical studies of the T 1 spin lifetime of the V Si defect in SiC, T 1 vs. temperature changes monotonically from 5 K to 300 K as a result of phonon-assisted spin relaxation mechanisms [20].…”

“…By contrast, the T 1 and T 2 * lifetimes of vacancy defects in SiC have been measured over a range of temperatures by at least two groups. The T 1 of Si vacancies decreased monotonically with increasing temperature [20], whereas the T 2 * of divacancies had a complicated, non-monotonic dependence [21].…”

“…A separate study on a similar sample, with Si vacancies formed through electron irradiation, showed T 2 times at room temperature of 160 μs [16]. Finally, a maximum coherence time on the order of hundreds of milliseconds was achieved at 17 K for Si vacancies using dynamic decoupling pulses [20].…”

<strong>Scalable fabrication of single silicon vacancy defect arrays in silicon carbide using focused ion beam</strong>

“…12 In particular, silicon vacancy (V Si ) defect in 4H-SiC has increasingly attracted attention owing to its excellent features, such as non-blinking single photon emission and long spin coherence times which persist up to room temperature (about 160 µs). 3,5,13 These remarkable properties have been exploited in many applications in quantum …”

“…3,5,13 These remarkable properties have been exploited in many applications in quantum photonics, 9,10 and quantum metrological studies such as high sensitivity magnetic sensing 14,15 and temperature sensing. 16 The V Si defect consists of a vacancy on a silicon site which exhibits a C 3v symmetry in 4H-SiC.…”