Strong tunable spin-spin interaction in a weakly coupled nitrogen vacancy spin-cavity electromechanical system
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2021-05-12 |
| Journal | Physical review. B./Physical review. B |
| Authors | Wei Xiong, Jiaojiao Chen, Bao‐Long Fang, Mingfeng Wang, Liu Ye |
| Institutions | Anhui University, Hefei University |
| Citations | 28 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research proposes a novel method to achieve strong, tunable spin-spin coupling between weakly interacting Nitrogen Vacancy (NV) centers in a hybrid quantum system, crucial for scalable quantum information processing.
- Core Achievement: Realization of effective strong spin-spin coupling (geff ~ 2π x 350 KHz) between two single NV centers, despite the initial weak coupling to the cavity (λ ~ 2π x 7 KHz).
- Methodology: A strongly driven electromechanical cavity generates two hybrid modes (polaritons). The system is tuned to a critical point where the NV spin selectively couples to the low-frequency polariton.
- Coupling Enhancement: The effective coupling strength (λ+) between the single NV spin and the low-frequency polariton is enhanced by approximately three orders of magnitude (reaching ~2π x 3.5 MHz).
- Quantum Bus: The low-frequency polariton acts as a robust quantum bus, mediating coherent quantum-information exchange between the two separated spin qubits.
- Gate Robustness: Numerical simulations confirm that the resulting iSWAP quantum gate maintains high fidelity, showing strong robustness against dissipation from the cavity, mechanical resonator, and spins, even at temperatures up to T ~ 20 mK.
- Probing Capability: The strong coupling allows for the measurement of the ac Stark shift of a single NV spin induced by a single polariton excitation, providing a feasible way to probe spin qubit states.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Initial Spin-Cavity Coupling (λ) | 2π x 7 | KHz | Estimated weak coupling (d = 50 nm) |
| Enhanced Spin-Polariton Coupling (λ+) | 2π x 3.5 | MHz | Achieved strong coupling regime |
| Coupling Enhancement Factor | 0.5 x 103 | Ratio | Relative enhancement of λ+ over λ |
| Effective Spin-Spin Coupling (geff) | 2π x 350 | KHz | Polariton-mediated coupling strength |
| Cavity Frequency (ωa) | ~2π x 2 | GHz | Estimated value |
| Mechanical Frequency (ωm) | ~2π x 70 | Hz | Estimated value |
| Cavity Quality Factor (Q) | 3 x 104 | Dimensionless | Typical gigahertz cavity |
| Cavity Decay Rate (κ) | 1 | MHz | Used for simulation |
| NV Transversal Relaxation Rate (γ⊥) | 1 | KHz | Used for simulation (γ⊥ << geff) |
| Operating Temperature (T) | ~20 | mK | Simulation temperature for nonzero thermal occupation (ntha = 0.01, nthm = 260) |
| NV Center Distance (d) | 50 | nm | Required distance for strong coupling feasibility |
| Zero-Field Splitting (D) | ≈ 2.87 | GHz | Triplet ground state of NV center |
Key Methodologies
Section titled “Key Methodologies”The strong spin-spin interaction is achieved by exploiting the critical behavior of a linearized electromechanical subsystem acting as a quantum bus.
- Hybrid System Linearization: A single NV spin is weakly coupled to an electromechanical cavity. A strong microwave driving field is applied to the cavity, linearizing the Hamiltonian and amplifying the electromechanical coupling strength (G).
- Polariton Mode Generation: The strong linearized coupling between the cavity and mechanical modes generates two hybrid modes: the high-frequency (ω+) and low-frequency (ω-) polaritons.
- Critical Point Tuning: The system is tuned to the critical point (G = Gc) by adjusting the driving field strength. At this point, the frequency of the low-frequency polariton vanishes (ω- → 0).
- Selective Coupling: Operating near the critical point, the NV spin is effectively decoupled from the high-frequency polariton (η+ ≈ 0). Simultaneously, the coupling strength to the low-frequency polariton (λ+) is dramatically enhanced due to the extremely small value of ω-.
- Quantum Bus Mediation: The low-frequency polariton, now strongly coupled to the NV spin, serves as a quantum bus. This polariton mediates an effective spin-spin interaction (Heff) between two separated NV centers placed in the dispersive regime.
- Quantum Gate Implementation: The resulting effective Hamiltonian is used to realize coherent quantum information exchange, specifically demonstrating the feasibility of an iSWAP gate (requiring gefft = π/2).
Commercial Applications
Section titled “Commercial Applications”The ability to realize robust, strong, and tunable spin-spin interactions in solid-state systems using electromechanical interfaces has direct implications for next-generation quantum technologies.
- Scalable Quantum Computing: Provides a feasible architecture for building scalable quantum networks using NV centers, leveraging their long coherence times and high tunability, connected via robust electromechanical buses.
- Solid-State Quantum Memory: The polariton-mediated coupling allows for coherent information transfer, essential for developing robust quantum memory elements based on NV spin qubits.
- High-Fidelity Quantum Gates: Enables the implementation of two-qubit gates (like iSWAP) that are highly robust against thermal noise and dissipation, crucial for reliable quantum computation in realistic environments (e.g., 20 mK cryostats).
- Quantum Metrology and Sensing: The ability to resolve the ac Stark shift induced by a single polariton excitation opens pathways for ultra-sensitive measurements of electric or magnetic fields using single NV spins.
- Advanced Diamond Materials: Requires high-purity, isotopically controlled diamond substrates with precise placement of NV centers, driving demand for advanced Chemical Vapor Deposition (CVD) techniques for material synthesis.
View Original Abstract
The long coherence time of a single nitrogen vacancy (NV) center spin in\ndiamond is a crucial advantage for implementing quantum information processing.\nHowever, the realization of strong coupling between single NV spins is\nchallenging. Here we propose a method to greatly enchance the interaction\nbetween two single NV spins in diamond which are only weakly coupled to an\nelectromechanical cavity. Owing to the presence of a critical point for the\nlinearized electromechanical subsystem, the coupling between a single NV spin\nand the high-frequency polariton (formed by the mechanical and cavity modes)\ncan be fully decoupled, but the coupling between the single NV spin and the\nlow-frequency polariton is however greatly enhanced. Thus, AC Stark shift of\nthe single NV spin can be measured. With the low-frequency polariton as a\nquantum bus, a strong coupling between two single NV centers is achievable.\nThis effective strong coupling can ensure coherent quantum-information exchange\nbetween two spin qubits in the weakly coupled spin-cavity elecromechanical\nsystem.\n