Quantum Control of the Tin-Vacancy Spin Qubit in Diamond
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2021-11-30 |
| Journal | Physical Review X |
| Authors | Romain Debroux, Cathryn P. Michaels, Carola M. Purser, Noel Wan, Matthew E. Trusheim |
| Institutions | Massachusetts Institute of Technology, DEVCOM Army Research Laboratory |
| Citations | 71 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research demonstrates successful multi-axis coherent control of the tin-vacancy (SnV) spin qubit in diamond using an all-optical stimulated Raman drive, establishing SnV as a highly competitive solid-state quantum interface.
- Core Value Proposition: The SnV center benefits from large spin-orbit coupling, offering robust protection against phonon-induced decoherence, allowing operation at 1.7 K (avoiding millikelvin requirements typical for SiV).
- Fast Coherent Control: Achieved a spin Rabi rate (Ω/2π) of 3.6(1) MHz via the all-optical Raman scheme, representing nearly three orders of magnitude improvement over previous direct microwave control attempts for SnV.
- Extended Coherence: The spin coherence time (T2) was dynamically decoupled using a CPMG-2 sequence, extending it to 0.33(14) ms, which is comparable to SiV results achieved at much lower temperatures (100 mK).
- High Fidelity Gates: The calculated π/2 gate fidelity is 92(4)%, limited primarily by excited-state optical scattering, which can be improved by increasing the single-photon detuning (Δ).
- Long Spin Lifetime: The electronic spin lifetime (T1) was measured at 15(1) ms, confirming that coherence is not limited by interorbital phonons at 1.7 K.
- Nuclear Register Access: Measured an electron-nuclear hyperfine coupling strength of 42.6(4) MHz for the intrinsic spin-active Sn isotope (I=1/2), enabling future quantum memory applications.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Operating Temperature | 1.7 | K | Closed-cycle cryostat |
| Magnetic Field Strength | 0.2 | T | Applied at 54.7° to SnV axis |
| Spin Rabi Rate (Ω/2π) | 3.6(1) | MHz | All-optical stimulated Raman drive |
| Inhomogeneous Dephasing (T2*) | 1.3(3) | µs | Measured via Ramsey interferometry |
| Coherence Time (T2) | 0.33(14) | ms | Extended via CPMG-2 dynamical decoupling |
| Spin Lifetime (T1) | 15(1) | ms | Measured under laser leakage |
| π/2 Gate Fidelity | 92(4) | % | Calculated, limited by optical scattering |
| Initialization Fidelity (Finit) | 99.6 | % | Achieved via resonant A1 transition drive |
| Hyperfine Coupling (A) | 42.6(4) | MHz | For spin-active Sn isotope (I=1/2) |
| Excited State Relaxation (Γ/2π) | 35 | MHz | Intrinsic linewidth |
| Saturation Power (Psat) | 4.6(7) | nW | For spin-cycling transition (A1) |
| Single-Photon Detuning (Δ/2π) | 1200 | MHz | Used for Rabi measurements (Fig. 2a) |
| Implantation Fluence (Sn+) | 109 | ions/cm2 | Sample fabrication |
| Implantation Energy | 350 | keV | Sample fabrication |
| Predicted Dopant Depth | 80(10) | nm | Below diamond surface |
Key Methodologies
Section titled “Key Methodologies”The experiment relies on high-quality diamond material processing and a novel all-optical control scheme utilizing microwave-modulated lasers.
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Sample Fabrication (Diamond Host):
- Material: Element6 CVD-grown type IIa diamond, characterized by ultra-low nitrogen and boron content (less than 5 ppb).
- Implantation: Sn+ ions were implanted at 350 keV with a fluence of 109 ions/cm2, targeting a shallow dopant depth of 80 nm.
- Annealing: Post-implantation annealing was performed at 1200 °C for two hours under high vacuum (less than 10-7 mbar) to activate the SnV centers.
- Cleaning: Residual graphite was removed using a boiling acid mixture (1:1:1 sulfuric, nitric, and perchloric acid).
- Nanostructuring: Nanopillars (radii 75 to 165 nm) were fabricated to enhance fluorescence collection efficiency and isolate individual emitters.
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Optical Lambda Scheme Implementation:
- Qubit Definition: The qubit is defined by the Zeeman-split electronic spin states in the lower orbital branch, |↓) and |↑).
- Raman Drive Generation: Two optical fields (ω1 and ω2) were generated as sidebands from a single 619 nm laser source using an amplitude electro-optic modulator (EOM).
- Control Mechanism: The EOM sidebands are controlled by an Arbitrary Waveform Generator (AWG) to set the Raman drive frequency (ωR = ω1 - ω2) and the relative phase (φ), allowing multi-axis control (x and y axes on the Bloch sphere).
- Stabilization: The EOM setpoint was stabilized using a lock-in amplifier and PID controller to maintain phase coherence between the sidebands.
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Coherent Control Sequences:
- Initialization/Readout: Qubit state preparation (polarization into |↑) or |↓)) and readout were achieved by resonant driving of the spin-cycling transitions (A1 or B2) using AOM-controlled pulses.
- Rabi Driving: Coherent spin rotation was demonstrated by applying the stimulated Raman drive, achieving 3.6 MHz Rabi oscillations.
- Ramsey Interferometry: Used to measure the inhomogeneous dephasing time (T2*) and the differential AC Stark shift (ΔAC). Serrodyne modulation (φ = τωs) was employed to recover the Ramsey signal periodically.
- Dynamical Decoupling: Hahn echo and CPMG-2 sequences were implemented using all-optical π pulses to suppress low-frequency magnetic noise from the 13C nuclear spin bath, extending T2 to the millisecond regime.
Commercial Applications
Section titled “Commercial Applications”The successful demonstration of fast, coherent, and long-lived spin control in SnV at elevated temperatures (1.7 K) positions this technology for several high-impact quantum applications.
- Quantum Networks and Repeaters:
- SnV serves as an efficient Spin-Photon Quantum Interface, capable of generating transform-limited photons entangled with a long-lived matter qubit.
- The ability to operate at 1.7 K simplifies cryogenics compared to SiV (which requires 100 mK), making deployment of Quantum Network Nodes more practical and cost-effective.
- Quantum Computing and Memory:
- The long T2 (0.33 ms) and T1 (15 ms) times, combined with fast gate speeds (3.6 MHz Rabi rate), make SnV a viable Solid-State Qubit.
- Access to the intrinsic Sn nuclear spin (42.6 MHz coupling) provides a pathway for developing a Nuclear Quantum Memory Register coupled to the electronic spin.
- Quantum Sensing (Magnetometry/Thermometry):
- The robust coherence properties enable high-sensitivity Optically Detected Magnetic Resonance (ODMR) sensing, potentially competitive with NV centers, but with superior optical properties.
- Integrated Photonics:
- SnV centers possess inversion symmetry, making them naturally compatible with Photonic Nanostructures (e.g., diamond waveguides and cavities), crucial for scaling up quantum circuits and enhancing light collection efficiency (already demonstrated >90% in related Group-IV centers).
View Original Abstract
<p>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.</p>