Fully robust qubit in atomic and molecular three-level systems
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2016-12-12 |
| Journal | New Journal of Physics |
| Authors | N. Aharon, I. Cohen, Fedor Jelezko, Alex Retzker |
| Institutions | UniversitÀt Ulm, Center for Integrated Quantum Science and Technology |
| Citations | 22 |
| Analysis | Full AI Review Included |
6CCVD Technical Analysis: Robust Qubit Coherence Enhancement in NV-Diamond
Section titled â6CCVD Technical Analysis: Robust Qubit Coherence Enhancement in NV-DiamondâBased on: âFully robust qubit in atomic and molecular three-level systemsâ (N Aharon et al 2016 New J. Phys. 18 123012)
Executive Summary
Section titled âExecutive SummaryâThis paper presents a groundbreaking method for constructing a fully robust qubit within a three-level system, specifically demonstrating its application using the Nitrogen-Vacancy (NV) center in diamond.
- Coherence Breakthrough: The scheme achieves robustness to both external magnetic noise and controller power fluctuations, resulting in a simulated coherence time ($T_{2}$) of $\sim 1820$ ”s.
- Performance Gain: This represents an improvement of more than two orders of magnitude ($\gt 200 \times$) over the baseline pure dephasing time ($T_{2}^{*} = 5$ ”s), pushing the qubit performance toward its fundamental lifetime limit.
- Material System: The methodology leverages the electronic ground state spin sub-levels of the NV-center, requiring high-quality Single Crystal Diamond (SCD) substrates.
- Novel Technique: Robustness is achieved via continuous off-resonant driving fields applied in a $\Lambda$ (three-level) configuration, simplifying implementation compared to traditional four-level continuous dynamical decoupling schemes.
- High-Value Application: The robust qubit enables enhanced quantum sensing, particularly for high-frequency AC magnetic signals, offering significantly improved sensitivity scaling ($ \sim \sqrt{T_{2}} $).
Technical Specifications
Section titled âTechnical SpecificationsâThe following parameters were utilized and achieved in the simulation of the NV-center implementation in diamond:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Material System | NV-Center in Diamond | N/A | Electronic spin 1 ground state sub-levels |
| Zero-Field Splitting ($D$) | 2.87 | GHz | Intrinsic characteristic of the NV-center |
| Static Magnetic Field ($g\mu_B B$) | $\sim 20$ | GHz | Applied for large Zeeman splitting ($ |
| Rabi Frequency ($\Omega$) | 70 | MHz | Amplitude of continuous driving fields |
| Primary Detuning ($\Delta_{1}$) | 500 | MHz | Optimized off-resonance parameter |
| Secondary Detuning ($\Delta_{2}$) | 209 | MHz | Optimized for robustness ($\Delta E_{0} = \Delta E_{B}$) |
| Energy Gap ($E_{BD}$) | $\sim 17.96$ | MHz | Energy separation of dressed states |
| Initial Dephasing Time ($T_{2}^{*}$) | 5 | ”s | Baseline coherence limited by ambient noise |
| Achieved Coherence Time ($T_{2}$) | $\sim 1820$ | ”s | Simulated result for fully robust qubit |
| Noise Reduction Mechanism | Continuous Dynamical Decoupling | N/A | Robustness to external magnetic and controller noise |
| Target Application | Quantum Sensing | N/A | Enhanced sensitivity to high-frequency signals |
Key Methodologies
Section titled âKey MethodologiesâThe robust qubit construction relies on a specific configuration and precise tuning of continuous driving fields applied to the NV-centerâs electronic ground state.
- Material Basis Selection: Utilization of the NV-center electronic spin ground state, $| m_{s} = 0 \rangle$ and $| m_{s} = \pm 1 \rangle$, which form a natural three-level system (a qutrit).
- Zeeman Splitting Application: A strong static magnetic field ($g\mu_B B \approx 20$ GHz) is applied along the NV axis to create a large Zeeman splitting between the $| \pm 1 \rangle$ states, resolving the $| \pm 1 \rangle \leftrightarrow | 0 \rangle$ transitions into two distinct frequencies ($\sim 23$ GHz and $\sim 17$ GHz).
- $\Lambda$ System Configuration: The three levels are coupled using continuous, off-resonant microwave driving fields, creating an effective robust qubit subspace (dressed states).
- Off-Resonant Driving Fields: The scheme utilizes red-detuned ($\Delta_{1}$) and blue-detuned ($\Delta_{2}$) microwave fields.
- $H_{red}$ (Red Detuned): Couples $| 0 \rangle$ to $| -1 \rangle$ and $| +1 \rangle$ with detuning $\Delta_{1}$.
- $H_{blue}$ (Blue Detuned): Couples $| 0 \rangle$ to $| -1 \rangle$ and $| +1 \rangle$ with detuning $\Delta_{2}$.
- Robustness Tuning: The ratio of the detunings ($\Delta_{1}$ and $\Delta_{2}$) and the Rabi frequency ($\Omega$) are precisely tuned to ensure the second-order Stark shifts of the two critical qubit states ($| 0 \rangle$ and $| B \rangle$) are identical. This eliminates first-order coupling to controller noise (driving amplitude fluctuations).
- High Energy Gap Maintenance: A large energy gap ($E_{BD} \approx 18$ MHz) is maintained between the robust qubit states and the non-qubit states, successfully mitigating the effects of external magnetic noise fluctuations.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâReplicating and advancing this breakthrough in robust quantum systems requires access to state-of-the-art diamond materials and advanced fabrication techniques. 6CCVD is uniquely positioned to supply the foundational materials and engineering support necessary for next-generation quantum sensing and computation.
Applicable Materials
Section titled âApplicable MaterialsâTo achieve the high $T_{2}$ performance demonstrated, the core material must minimize crystal defects and strain that cause inhomogeneous broadening and limit coherence.
| 6CCVD Material Recommendation | Grade | Key Capability Connection |
|---|---|---|
| Electronic Grade Single Crystal Diamond (SCD) | Quantum/Optical | Required for ultra-low concentration of substitutional nitrogen ([N] < 1 ppb) to ensure maximum NV center stability and initial $T_{2}^{*}$. |
| High-Purity SCD Substrates | Low-Strain | Minimal birefringence and internal stress, crucial for maintaining the precise energy level separations (Zeeman splitting) required for off-resonant driving. |
| Custom NV Creation | Engineering Service | While NV creation is typically done post-growth (implantation/annealing), 6CCVD ensures the precursor material quality (low [N]) is optimal for high-fidelity NV defect creation and controlled spin manipulation. |
Customization Potential
Section titled âCustomization PotentialâNV-center experiments, particularly those involving microwave manipulation, require precise integration of the diamond substrate with external hardware.
- Custom Dimensions: 6CCVD supplies inch-sized plates/wafers (up to 125mm PCD) and custom SCD slices, allowing researchers to choose optimal geometries for their microwave transmission lines (e.g., CPW structures).
- Thickness Control: We offer SCD thickness control from 0.1 ”m up to 500 ”m, critical for optimizing microwave field coupling and minimizing absorption losses in sensing applications.
- Advanced Metalization Services: The implementation of the driving fields often requires fabrication of microwave structures directly onto the diamond. 6CCVD provides in-house metalization using a wide range of materials, including: Ti/Pt/Au, Ti/W/Cu, or custom stacks, tailored for specific microwave frequencies ($\sim 17-23$ GHz in this case).
- Surface Preparation: Achieving high-fidelity optical and microwave coupling requires atomically flat surfaces. Our advanced polishing capabilities deliver Ra < 1 nm (SCD), ensuring minimal surface scattering losses for optical initialization and readout.
Engineering Support
Section titled âEngineering SupportâThe robust qubit scheme requires precise parameter optimization ($\Delta_{1} / \Delta_{2}$ ratio and $\Omega$). Success hinges on the quality and consistency of the host diamond.
6CCVDâs in-house PhD engineering team specializes in diamond material physics and defect engineering. We provide dedicated assistance with material selection for similar NV-center based Quantum Sensing or Quantum Information Processing projects, advising on optimal nitrogen concentration, crystallographic orientation, and surface termination to maximize qubit performance.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract We present a new method of constructing a fully robust qubit in a three-level system. By the application of continuous driving fields, robustness to both external and controller noise is achieved. Specifically, magnetic noise and power fluctuations do not operate within the robust qubit subspace. Whereas all the continuous driving based constructions of such a fully robust qubit considered so far have required at least four levels, we show that in fact only three levels are necessary. This paves the way for simple constructions of a fully robust qubit in many atomic and solid state systems that are controlled by either microwave or optical fields. We focus on the NV-center in diamond and analyze the implementation of the scheme, by utilizing the electronic spin sub-levels of its ground state. In current state-of-the-art experimental setups the scheme leads to improvement of more than two orders of magnitude in coherence time, pushing it towards the lifetime limit. We show how the fully robust qubit can be used to implement quantum sensing, and in particular, the sensing of high frequency signals.