Towards a Room-Temperature Spin Quantum Bus in Diamond via Electron Photoionization, Transport, and Capture
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2016-11-18 |
| Journal | Physical Review X |
| Authors | M.âW. Doherty, C.âA. Meriles, A. Alkauskas, Fedder H, M.âJ. Sellars |
| Institutions | Centre for Quantum Computation and Communication Technology, City College of New York |
| Citations | 31 |
| Analysis | Full AI Review Included |
6CCVD Technical Analysis: Room-Temperature Spin Quantum Bus in Diamond
Section titled â6CCVD Technical Analysis: Room-Temperature Spin Quantum Bus in DiamondâExecutive Summary
Section titled âExecutive SummaryâThis technical analysis of the research paper âTowards a room-temperature spin quantum bus in diamond via optical spin injection, transport and detectionâ highlights a critical pathway toward scalable, solid-state Quantum Information Processing (QIP) using MPCVD diamond.
- Core Achievement: Proposes a feasible architecture for an on-chip spin quantum bus utilizing coherent electrical spin transport between distant spin registers in diamond at ambient temperatures.
- Mechanism Focus: The protocol relies on engineered Nitrogen-Vacancy ($NV^-$) and Nitrogen substitutional ($^{14}N_s$) defect pairs to enable high-fidelity optical spin injection and detection.
- Material Imperative: Achieving the necessary coherent transport requires Ultra-High Purity Single Crystal Diamond (SCD) to maintain the predicted intrinsic electron spin relaxation time ($T_{1}$) of $\sim 180$ ns.
- Key Engineering Challenge: The primary barrier is adequately confining the electron probability density during transport to ensure rapid capture ($\lt; 100$ ns) at the receiving cluster.
- Proposed Solution: Diamond nanowire structures (lateral dimensions $l \ge 0.2$ ”m) combined with high electric fields ($E \ge 63$ mV/”m) are identified as the necessary strategy for sufficient electron confinement.
- 6CCVD Value: 6CCVD provides the necessary Optical Grade SCD substrates, custom defect engineering (implantation), advanced laser processing for nanowire fabrication, and tailored metalization required to realize this complex quantum architecture.
Technical Specifications
Section titled âTechnical SpecificationsâThe realization of the room-temperature spin quantum bus is contingent upon meeting the following hard constraints derived from diamondâs intrinsic properties and experimental design:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Electron Spin Relaxation Time ($T_{1}$) | $\sim 180$ | ns | Intrinsic limit for high-purity diamond at room temperature. Defines max transport time. |
| Maximum Transport Time | $\le 80$ | ns | Allocated time for transport, ensuring total process (injection+transport+capture) is $\lt; 180$ ns. |
| Maximum Transport Distance | $\sim 2$ | mm | Achievable in high-purity diamond under electric field $E \sim 100$ V/cm. |
| Required Capture Time ($\Gamma_{cap}$) | $\lt; 100$ | ns | Target for efficient spin capture by $^{14}N^+_s$ center. |
| Required Electron Density ($\rho$) at Capture Site | $\gt; 50$ | $\mu$m-3 | Density needed to achieve required $\Gamma_{cap} \lt; 100$ ns. |
| Background $N_s$ Impurity Density | $\le 10$ | $\mu$m-3 | Maximum concentration to prevent spurious electron capture during transport. |
| Nanowire Lateral Dimension ($l$) | $\ge 0.2$ | $\mu$m | Minimum dimension required for effective electron confinement. |
| Required Electric Field ($E$) for $l=0.2$ $\mu$m Nanowire | $\ge 63$ | mV/$\mu$m | Needed to achieve adequate drift speed and confinement. |
| NV$^{-}$ Photoionization Energy (Optimal) | $2.8 - 3.1$ | eV | One-photon absorption range for high-fidelity coherent spin injection. |
| Magnetic Field Strength ($B$) | $\sim 5000$ | G | Required to suppress non-secular electron spin terms and minimize nuclear spin flip rates. |
| Required NV- $^{14}N_s$ Dipolar Coupling | $\sim 10$ | MHz | Necessary for fast two-qubit gates ($\lt; 100$ ns) during spin preparation. |
Key Methodologies
Section titled âKey MethodologiesâThe proposed protocol for room-temperature coherent spin transport relies on tight integration of optical control, microwave pulses, and precise material engineering using $NV^-$ and $^{14}N_s$ defects:
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NV- $^{14}N_s$ Cluster Initialization:
- Initialize $NV^-$ electron spin and charge state optically (Green pulse, $\sim 500$ ns).
- Prepare $^{14}N_s$ in the neutral charge state ($N^0_s$) and initialize its nuclear spin into the $m_I = 0$ projection using microwave control and red optical pulses (1.7-1.946 eV) to facilitate recharge from neighboring N$_s$ ensembles.
- Apply a large magnetic field ($B \sim 5000$ G) to minimize electron spin dephasing caused by nuclear spin fluctuations.
-
Coherent Spin Injection (Preparation & Photoionization):
- Use the NV$^-$ electron spin and microwave pulses ($\sim 100$ ns) to coherently prepare the $^{14}N_s$ electron spin into the desired quantum state ($\vert \psi \rangle$).
- Inject the prepared electron spin into the conduction band via one-photon photoionization of the $^{14}N_s$ donor center using a Red Optical Pulse. This must occur within the $\lt; 1$ ”s constraint set by the $^{14}N_s$ nuclear spin dephasing time.
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Controlled Drift-Diffusion Transport:
- Transport the electron across the chip, relying on the intrinsic diamond $T_{1} \sim 180$ ns spin lifetime.
- Utilize a diamond nanowire architecture (lateral dimension $l \ge 0.2$ ”m) and high applied electric fields ($E \ge 63$ mV/”m) to confine the electron probability density ($\rho$).
- The electric field drives the electron at speeds $\ge 28$ ”m/ns, ensuring that the required capture concentration is maintained and transport occurs in the allotted $\lt; 80$ ns window.
-
Spin Capture and Optical Detection:
- The electron is captured by an ionized $^{14}N^+_s$ center at the receiving cluster B ($\sim 100$ ns capture time required).
- The captured spin state of the newly formed $N^0_s$ center is coherently read out using two-qubit gates mediated by the proximal NV$^-$ B center, followed by optical readout.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research demands extremely high material quality and advanced nano-fabrication capabilities, directly aligning with 6CCVDâs specialization in high-purity MPCVD diamond and customization services.
| Research Requirement | 6CCVD Solution & Capability | Core Value Proposition |
|---|---|---|
| Ultra-High Purity Substrates (Low $N_s$ for $T_{1} \sim 180$ ns) | Optical Grade Single Crystal Diamond (SCD): MPCVD growth tuned to achieve substitutional nitrogen concentration ($\text{N}_s$) well below the required $\le 10$ $\mu$m$^{-3}$ ($\lt; 1$ ppb) threshold. | Guarantees the maximum intrinsic spin coherence time ($T_{1}$) essential for long-distance, room-temperature spin transport. |
| Custom Defect Engineering ($NV^-$ - $^{14}N_s$ pairs, $\sim 1.5$ nm spacing) | Precision Ion Implantation Services: Customized defect introduction to create localized NV and $^{14}N_s$ clusters with high spatial fidelity, ensuring dipolar coupling $\sim 10$ MHz for fast gates. | Enables the crucial two-qubit operations required for high-fidelity coherent spin injection and detection protocols within the strict $\lt; 1$ $\mu$s time limits. |
| Nanowire Fabrication & Scalability (Dimensions down to $l=0.2$ $\mu$m) | Advanced Laser Cutting and Etching: Provides custom dimension Plates/wafers up to $125$ mm (PCD) and substrates up to $10$ mm thick. Services include laser cutting for initial device topology and precision polishing (Ra $\lt; 1$ nm for SCD). | Delivers the robust, large-format diamond platform necessary for subsequent top-down fabrication of nanowire arrays required for electron confinement. |
| Spin Control Electrodes (Requirement for applied $E$ fields $\ge 63$ mV/$\mu$m) | In-House Custom Metalization: Capability to deposit complex metal stacks (Au, Pt, Pd, Ti, W, Cu) with high-resolution patterning for end and lateral transport control electrodes and surface microwave lines. | Accelerates device development by providing fully metalized quantum substrates ready for electrical control and high-speed QIP experimentation. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD material science and engineering team specializes in the growth and characterization of defect-rich MPCVD diamond optimized for quantum applications. We offer consultation to researchers replicating or extending this room-temperature spin transport research, focusing specifically on optimizing ultra-low nitrogen concentration and implementing custom implantation strategies for NV and $N_s$ pairing.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Diamond is a proven solid-state platform for spin-based quantum technology. \nThe nitrogen-vacancy (NV) center in diamond has been used to realize \nsmall-scale quantum information processing (QIP) and quantum sensing under \nambient conditions. A major barrier in the development of large-scale QIP in \ndiamond is the connection of NV spin registers by a quantum bus at room \ntemperature. Given that diamond is expected to be an ideal spin transport \nmaterial, the coherent transport of spin directly between the spin registers \noffers a potential solution. Yet, there has been no demonstration of spin \ntransport in diamond due to difficulties in achieving spin injection and \ndetection via conventional methods. Here, we exploit detailed knowledge of the \nparamagnetic defects in diamond to identify novel mechanisms to achieve spin \ninjection, transport and detection in diamond at room temperature. Having \nidentified these mechanisms, we explore how they may be combined to realise an \non-chip spin quantum bus.