Efficient and robust signal sensing by sequences of adiabatic chirped pulses
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2020-08-07 |
| Journal | Physical Review Research |
| Authors | Genko T. Genov, Yachel Ben-Shalom, Fedor Jelezko, Alex Retzker, Nir Bar‐Gill |
| Institutions | Hebrew University of Jerusalem, Center for Integrated Quantum Science and Technology |
| Citations | 17 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research proposes and experimentally validates a novel quantum sensing scheme, RAP-XY8 (Rapid Adiabatic Passage combined with XY8 dynamical decoupling), demonstrating superior performance for AC magnetic field sensing using Nitrogen-Vacancy (NV) centers in diamond.
- Core Innovation: The scheme uses phased, adiabatic, chirped pulses (RAP) instead of standard rectangular pulses. These pulses act as a double filter, rectifying the signal and partially removing frequency noise, while sudden phase changes compensate for non-adiabatic errors.
- Coherence Time Improvement: Numerical simulations showed a T2 improvement from approximately 14 µs (standard XY8) to 1.7 ms (RAP-XY8) in systems with large inhomogeneous broadening.
- Experimental Sensitivity Gain: Direct measurements showed a 30% improvement in magnetic sensitivity, achieving ηRAP = 33 ± 6 nT·Hz-1/2 compared to ηXY8 = 43 ± 6 nT·Hz-1/2 under optimized conditions.
- Robustness: RAP-XY8 maintains high coherence times (T2 ≈ 1.9 ms) and sensitivity even when subjected to amplitude noise or when operating at low Rabi frequencies, conditions where standard XY8 performance degrades significantly (up to 45% drop in T2).
- Applicability: The technique is highly robust to large inhomogeneous broadening and driving field inhomogeneity, making it suitable for NV ensembles, NV nanodiamonds in cells, and other solid-state quantum platforms.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV Density (Sample) | ~10 | ppb | Standard-grade diamond (Element Six) |
| NV T1 Lifetime | 5.8 ± 0.6 | ms | Measured NV spin property |
| NV T2 Dephasing Time* | 34 ± 14 | ns | Measured NV spin property |
| Hahn Echo T2 | 198 ± 18 | µs | Measured NV spin property |
| Inhomogeneous Broadening | 2π × (2.1 ± 0.1) | MHz | Measured NV property |
| Peak Rabi Frequency (High Rabi) | 2π 5 | MHz | Experimental control field (Ω0) |
| Peak Rabi Frequency (Low Rabi) | 2π 1.7 | MHz | Experimental control field (Ω0) |
| RAP Chirp Range (Optimized) | 2π 40 | MHz | High Rabi experiment (R) |
| RAP Characteristic Time Ratio (Optimized) | 0.17 | T/Tpulse | High Rabi experiment |
| Coherence Time (RAP-XY8, High Rabi) | 1943 ± 231 | µs | Experimental T2 (robust performance) |
| Coherence Time (XY8, High Rabi) | 1811 ± 184 | µs | Experimental T2 (optimized performance) |
| Coherence Time (XY8, Low Rabi) | 1057 ± 149 | µs | Experimental T2 (degraded performance) |
| Optimal Sensitivity (RAP-XY8, Direct) | 33 ± 6 | nT·Hz-1/2 | Direct measurement |
| Optimal Sensitivity (XY8, Direct) | 43 ± 6 | nT·Hz-1/2 | Direct measurement |
| Sensed AC Field Frequency (Example) | 2π 43.8 | kHz | Half the pulse repetition rate (ωs) |
| Sensed AC Field Amplitude (Example) | 78 | nT | High Rabi experiment |
Key Methodologies
Section titled “Key Methodologies”The experimental demonstration of RAP sensing was conducted on an ensemble of NV centers in diamond using a home-built confocal fluorescence microscope setup.
-
Sample and Preparation:
- A standard-grade diamond sample (Element Six) containing NV ensembles (~10 ppb density) was used.
- The NV electron spin was initialized into the |0> state via optical pumping using 532 nm green light.
- A bias magnetic field (332 Gauss) was applied to define the quantization axis.
-
Microwave Control and Pulse Generation:
- Microwave (MW) control fields were generated using an Arbitrary Waveform Generator (AWG - Tektronix AWG70002A, 16 Gs sampling rate).
- The AWG was used to create the complex, time-dependent Rabi frequency Ω(t) and detuning Δ(t) profiles required for the Rapid Adiabatic Passage (RAP) pulses, following the Allen-Eberly model.
-
Pulse Sequence Implementation:
- The RAP pulses were incorporated into the widely used XY8 dynamical decoupling sequence (RAP-XY8).
- The RAP pulse parameters (characteristic time T and chirp range R) were experimentally optimized to maximize the dynamical decoupling efficiency (T2).
- The sequence was tested under three conditions: High Rabi frequency (2π 5 MHz), High Rabi with added Gaussian amplitude noise (width 0.2 Ω0), and Low Rabi frequency (2π 1.7 MHz).
-
AC Field Sensing:
- An external AC magnetic signal was generated using a home-built coil driven by a function generator.
- The AC field frequency (ωs) was matched to half the pulse repetition rate (Tpulse + τ = π/ωs) to maximize the filter function response.
-
Readout and Analysis:
- The NV spin state was read out optically via spin-dependent fluorescence (650-800 nm).
- Fluorescence difference measurements were recorded after applying the DD sequence to determine the coherence time (T2) and the accumulated phase (for sensitivity η).
- Sensitivity (η) was calculated indirectly from the coherence decay curves and directly from the maximal slope of the fluorescence signal versus magnetic field amplitude.
Commercial Applications
Section titled “Commercial Applications”The robust and efficient quantum sensing demonstrated by the RAP-XY8 protocol is critical for applications requiring high-fidelity measurements in noisy, inhomogeneous environments.
| Industry/Field | Application Relevance | Technical Advantage of RAP-XY8 |
|---|---|---|
| Quantum Sensing & Metrology | High-precision magnetic field mapping, current sensing, and weak signal detection. | Achieves significantly longer coherence times (T2) and higher sensitivity (30% improvement) than standard methods. |
| Solid-State Quantum Computing | Robust control and decoupling of qubits in solid-state systems (e.g., NV centers, trapped ions). | Robustness against large inhomogeneous broadening and amplitude/frequency noise, crucial for scaling up quantum processors. |
| Materials Science & Characterization | Nanoscale NMR/ESR, characterization of magnetic materials, and sensing in complex biological environments. | Applicable in systems with substantial driving field inhomogeneity (e.g., NV nanodiamonds in cells) where control fields are non-uniform. |
| Medical Diagnostics (MRI/NMR) | Development of highly sensitive, compact magnetic resonance systems. | The broad bandwidth and robustness allow for sensing of weaker fields and improved precision due to longer achievable coherence times. |
| Advanced Microwave Engineering | Design and testing of robust control sequences for complex quantum systems. | Provides a proven, phased pulse sequence that compensates for non-adiabatic couplings and pulse imperfections. |
View Original Abstract
We propose a scheme for sensing of an oscillating field in systems with large inhomogeneous broadening and driving field variation by applying sequences of phased, adiabatic, chirped pulses. These act as a double filter for dynamical decoupling, where the adiabatic changes of the mixing angle during the pulses rectify the signal and partially remove frequency noise. The sudden changes between the pulses act as instantaneous π pulses in the adiabatic basis for additional noise suppression. We also use the pulses’ phases to correct for other errors, e.g., due to nonadiabatic couplings. Our technique improves significantly the coherence time in comparison to standard XY8 dynamical decoupling in realistic simulations in NV centers with large inhomogeneous broadening. Beyond the theoretical proposal, we also present proof-of-principle experimental results for quantum sensing of an oscillating field in NV centers in diamond, demonstrating superior performance compared to the standard technique.