Observing Information Backflow from Controllable Non-Markovian Multichannels in Diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-05-27 |
| Journal | Physical Review Letters |
| Authors | Ya-Nan Lu, Yu-Ran Zhang, GangâQin Liu, Franco Nori, Heng Fan |
| Institutions | RIKEN, University of Chinese Academy of Sciences |
| Citations | 44 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates the experimental engineering and characterization of controllable non-Markovian dynamics in a solid-state quantum system using a Nitrogen-Vacancy (NV) center in diamond.
- Core Achievement: Successful engineering of multiple, controllable dissipative channels (noise sources) using adjacent nuclear spins (14N and 13C) coupled to the NV electron spin.
- Non-Markovianity Witness: The study utilizes Quantum Fisher Information (QFI) flow as a metric to characterize the non-Markovian behavior, observing information backflow from the engineered environment to the open system.
- Metrological Utility: The QFI flow is decomposed into subflows corresponding to individual dissipative channels, allowing for channel-specific analysis of non-Markovianity, which is crucial for noisy quantum metrology.
- Entanglement Preservation: The metrologically useful entanglement (QFI > 2) of a two-qubit system (electron spin + 13C spin) was shown to survive for extended periods despite being subject to spin bath noise.
- Material System: Experiments were conducted on a high-purity bulk diamond NV center at ambient conditions, demonstrating robust solid-state quantum control.
- Key Finding: The measure of non-Markovianity calculated from the sum of QFI subflows quantifies the memory effects more effectively than the measure derived from the total QFI flow when multiple channels are active.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Material Purity (N concentration) | < 5 | p.p.b. | High-purity bulk diamond (Element Six) |
| NV Center Depth | 10 | ”m | Below diamond surface |
| Excitation Wavelength | 532 | nm | Green laser pulse |
| Excitation Power | 240 | ”W | Laser power for optical pumping |
| Photon Detection Rate | 450 | kcps | Signal rate using solid immersion lenses (SILs) |
| External Magnetic Field (Bz) | 482 | Gauss | Along NV axis for polarization/manipulation |
| NV Zero-Field Splitting (A) | ~ 2.87 | GHz | Ground spin triplet splitting |
| 14N Hyperfine Coupling (An) | ~ -2.16 | MHz | Electron spin to host 14N spin |
| 13C Hyperfine Coupling (Ac) | ~ 12.8 | MHz | Electron spin to proximal 13C spin |
| 13C RF Pulse Frequency | 13.284 | MHz | Resonant frequency for manipulation |
| 14N RF Pulse Frequency | 2.929 | MHz | Resonant frequency for manipulation |
| NV Electron Spin Rabi Frequency | 23.8 | MHz | Measured oscillation rate |
| NV Electron Spin Coherence Time (T2*) | ~ 2.9 | ”s | Measured via Ramsey signal fitting |
| QFI Envelope Decay Time (T2) | ~ 1026 | ns | Fit parameter for spin bath influence (QR(t)) |
| Maximum QFI Observed | 3.687 | Dimensionless | Achieved for maximally entangled two-qubit state (QFI > 2 indicates metrological utility) |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relies on precise control and measurement of a three-qubit register (NV electron spin, 14N nuclear spin, 13C nuclear spin) embedded in diamond.
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Sample Preparation and Setup:
- Utilized high-purity bulk diamond containing NV centers 10 ”m below the surface.
- Solid immersion lenses (SILs) were etched onto the surface to enhance photon collection efficiency.
- An external magnetic field (B = 482 Gauss) was applied along the NV symmetry axis to lift spin degeneracy and enable selective manipulation.
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Spin Polarization and Initialization:
- The three-qubit system was polarized to an initial state (e.g., |0>e|â>n|â>c) using a short 532 nm laser pulse, leveraging the Excited-State Level Anti-Crossing (ESLAC) mechanism.
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Quantum State Preparation:
- Microwave (MW) and resonant Radio-Frequency (RF) pulses (13.284 MHz for 13C, 2.929 MHz for 14N) were applied to prepare the open system (electron spin alone or electron spin + 13C spin) in a desired initial state, such as a superposition state (|+)e) or a maximally entangled state.
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Dissipative Channel Control:
- The 14N and 13C nuclear spins acted as controllable dissipative channels. Their influence (open or closed) on the electron spin dynamics was controlled by tuning the durations of the RF pulses (adjusting parameters Ï1 and Ï2).
- The remaining weakly coupled 13C nuclear spins acted as an uncontrollable Markovian spin bath.
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Time Evolution and Tomography:
- The open system was allowed to undergo free evolution under the influence of the controlled and uncontrolled channels.
- State tomography (single-qubit and two-qubit) was performed at different evolution durations using sequences involving MW and RF transfer pulses to reconstruct the density matrix.
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QFI and Non-Markovianity Analysis:
- The Quantum Fisher Information (QFI) was calculated from the reconstructed density matrix.
- The QFI flow, I(t) = dQ/dt, was calculated and smoothed using adjacent average smoothing.
- The total QFI flow was decomposed into subflows (In, Ic, IR) corresponding to the 14N, 13C, and spin bath channels, respectively, to quantify the non-Markovianity (N(t)) based on the sum of inward QFI subflows.
Commercial Applications
Section titled âCommercial ApplicationsâThis research, focused on controlling noise and information flow in solid-state quantum systems, has direct relevance to several high-tech engineering and commercial sectors:
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Quantum Computing and Registers:
- Application: Developing robust quantum processors and memory elements.
- Relevance: The ability to engineer and mitigate specific noise channels (non-Markovian dynamics) is critical for increasing qubit coherence times and fidelity in solid-state spin registers, such as those based on NV centers.
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Quantum Metrology and Sensing:
- Application: Ultra-high precision sensors for magnetic fields, temperature, and rotation.
- Relevance: Non-Markovian dynamics can sometimes enhance metrological precision (as QFI is preserved or revived). This work provides a framework for designing optimal sensing protocols that leverage or suppress specific environmental noise characteristics.
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Advanced Diamond Materials:
- Application: Production of high-purity, defect-engineered diamond substrates.
- Relevance: The experiments rely on high-quality, low-nitrogen concentration bulk diamond (Element Six). Control over NV center location and coupling to specific nuclear spins drives demand for advanced CVD growth techniques capable of precise defect incorporation and isotopic control (e.g., 12C enrichment).
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Solid-State Physics Research Tools:
- Application: Creating controllable quantum simulators.
- Relevance: The engineered system serves as a platform to study fundamental open quantum system dynamics, providing a testbed for theoretical models of decoherence and memory effects in condensed matter.
View Original Abstract
The unavoidable interaction of a quantum open system with its environment leads to the dissipation of quantum coherence and correlations, making its dynamical behavior a key role in many quantum technologies. In this Letter, we demonstrate the engineering of multiple dissipative channels by controlling the adjacent nuclear spins of a nitrogen-vacancy center in diamond. With a controllable non-Markovian dynamics of this open system, we observe that the quantum Fisher information flows to and from the environment using different noisy channels. Our work contributes to the developments of both noisy quantum metrology and quantum open systems from the viewpoints of metrologically useful entanglement.