Selective noise resistant gate
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-12-07 |
| Journal | Physical review. B./Physical review. B |
| Authors | Jonatan Zimmermann, Paz London, Yaniv Yirmiyahu, Fedor Jelezko, Aharon Blank |
| Institutions | UniversitĂ€t Ulm, Technion â Israel Institute of Technology |
| Citations | 4 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThe research introduces the Selective Noise Resistant Gate (SNRG) protocol, a novel method for achieving high-fidelity, selective control of individual spin qubits in dense solid-state quantum registers, overcoming the inherent trade-off between noise protection and spectral selectivity.
- Core Innovation: SNRG combines Dynamical Decoupling (DD) sequences with pulsed, alternating magnetic field gradients to protect the qubit coherence (high fidelity) while preserving the spectral separation (high selectivity).
- Performance Achieved (NV Center): The SNRG scheme demonstrated a state fidelity (F) of 0.9 ± 0.02 for a pi-x gate.
- Selectivity Enhancement: The spectral bandwidth (BW) was measured at 49 ± 5 kHz, nearly an order of magnitude narrower than the unprotected Rabi gate bandwidth.
- Noise Mitigation: The protocol extends the effective coherence time from the short dephasing time (T2* â 5 ”s) toward the longer protected decoherence time (T2).
- Gradient Requirement Reduction: The scheme enables selective control using relatively moderate magnetic gradients, projecting a future requirement of only 1 mG/nm for high-density registers (10 nm separation).
- Scalability: The SNRG protocol is readily extendable to 2D arrays, trapped ions, neutral atoms, and high-resolution imaging of dense spin systems.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Qubit System | Single NV Center | N/A | Electronic spin in diamond ( |
| Qubit Splitting | ~1.8 | GHz | Zero-field splitting between qubit states |
| Diamond Type | IIa, electronic grade | N/A | Nitrogen concentration less than 5 ppb; natural 13C abundance |
| Static Magnetic Field (B0) | Estimated 380 | G | Generated by external SmCo magnet |
| Rabi Frequency (Ω) | 54 | kHz | On-resonance driving frequency |
| SNRG Gate Fidelity (F) | 0.9 ± 0.02 | N/A | Output state fidelity after pi-x gate |
| SNRG Bandwidth (BW) | 49 ± 5 | kHz | Spectral selectivity achieved (equivalent to 20 mG) |
| Unprotected Rabi Fidelity | 0.27 ± 0.1 | N/A | Continuous driving Rabi gate |
| Dephasing Time (T2*) | 5 ± 1 | ”s | Dominated by 13C nuclear spin bath |
| Noise Coupling Strength (b) | 42 | kHz | Fitted Ornstein-Uhlenbeck noise parameter |
| Noise Correlation Time (tc) | 230 | ”s | Fitted Ornstein-Uhlenbeck noise parameter |
| Microwire Width | 15 | ”m | Used for microwave driving and gradient generation |
| Gradient Calibration | 0.93 | MHz/V | Frequency shift per 1 V AWG driving voltage |
| Projected Gradient Need | 1 | mG/nm | Required for future BW = 5 kHz (10 nm spin separation) |
Key Methodologies
Section titled âKey MethodologiesâThe Selective Noise Resistant Gate (SNRG) protocol is implemented by combining robust Dynamical Decoupling (DD) sequences with engineered magnetic field modulation.
- Qubit System Preparation: A single Nitrogen-Vacancy (NV) center in a Type IIa diamond crystal is used. The qubit is isolated between the |ms = 0> and |ms = -1> states, separated by approximately 1.8 GHz.
- Physical Setup: Microwave driving and magnetic field gradients are applied via two crossing 15 ”m microwires stretched across the diamond surface, placed in close proximity (20 ”m) to the NV center.
- Gate Segmentation and DD: The desired quantum gate (pi-x rotation) is divided into N segments. A robust DD sequence (e.g., XY-8) consisting of pi pulses is interleaved between these segments to cancel the effects of slow magnetic noise (ÎŽ) and extend the coherence time (T2).
- Gradient Modulation (SNRG Core): Unlike standard Dynamically Protected Gates (DPG) where the gradient is canceled by DD, the SNRG scheme alternates the longitudinal magnetic field (Bz) gradient between positive (+Îz) and negative (-Îz) values after each DD inversion pulse.
- This modulation ensures that the noise (ÎŽ) is canceled, but the gradient-induced detuning (Îz) constructively accumulates, preserving spectral selectivity.
- Frequency Modulation (FM) Driving: Since the Bz field is switched during the sequence, the microwave driving frequency and phase must be modulated (FM) to continuously follow the instantaneous axis of the resonant spin, ensuring uninterrupted rotation.
- Phase Cycling for Robustness: To handle noncommutability issues arising from multi-axis DD sequences (like XY-8), the microwave driving phase is inverted (phase cycling) after each uncommutable DD operator (e.g., Ïy pulse) to ensure constructive accumulation of the desired rotation.
- Fidelity Measurement: Fidelity and bandwidth are measured by scanning the magnetic field gradient (which controls the detuning Îz) while fixing the microwave frequency dynamics, and measuring the Sz spin projection at the end of the gate sequence.
Commercial Applications
Section titled âCommercial ApplicationsâThe ability to selectively control individual qubits in a dense, noisy environment is critical for scaling solid-state quantum technology.
- Solid-State Quantum Computing:
- Enabling the construction of scalable quantum registers based on interacting spin arrays (e.g., NV centers or silicon carbide defects) where qubits are closely spaced (e.g., 10 nm) and require individual addressing.
- Facilitating robust two-qubit gates by ensuring the dipolar interaction is stronger than the decoherence rate, while maintaining individual control.
- High-Resolution Quantum Sensing and Imaging:
- Developing high-resolution magnetic resonance imaging (MRI) or sensing of dense spin systems (e.g., biological samples or materials) by allowing selective manipulation of spins within a small volume, overcoming the diffraction limit.
- Quantum Communication:
- Providing highly selective and robust control over spin qubits used as memory nodes in quantum networks.
- Atomic and Ion Systems:
- The SNRG scheme is directly extendable to other atom-like systems, including trapped ions and neutral atoms, where selective addressing via magnetic gradients is employed.
View Original Abstract
Realizing individual control on single qubits in a spin-based quantum\nregister is an ever-increasing challenge due to the close proximity of the\nqubits resonance frequencies. Current schemes typically suffer from an inherent\ntrade-off between fidelity and qubits selectivity. Here, we report on a new\nscheme which combines noise protection by dynamical decoupling and magnetic\ngradient based selectivity, to enhance both the fidelity and the selectivity.\nWith a single nitrogen-vacancy center in diamond, we experimentally demonstrate\nquantum gates with fidelity = 0.9 $\pm$ 0.02 and a 50 kHz spectral bandwidth,\nwhich is almost an order of magnitude narrower than the unprotected bandwidth.\nOur scheme will enable selective control of an individual nitrogen-vacancy\nqubit in an interacting qubits array using relatively moderate gradients of\nabout 1 mG/nm.\n