High-fidelity transfer and storage of photon states in a single nuclear spin

At a Glance

Metadata	Details
Publication Date	2016-06-06
Journal	Nature Photonics
Authors	Sen Yang, Ya Wang, D. D. Bhaktavatsala Rao, Thai Hien Tran, Ali S. Momenzadeh
Institutions	Yokohama National University, University of Stuttgart
Citations	135
Analysis	Full AI Review Included

Technical Documentation & Analysis: High Fidelity Photon Storage in NV Diamond

Executive Summary

This research demonstrates a crucial advancement toward practical, scalable quantum repeater networks by achieving high-fidelity, long-duration storage of a photon state within a single solid-state nuclear spin qubit in diamond.

Core Achievement: Coherent transfer and heralded storage of a photon polarization state into the intrinsic ¹⁴N nuclear spin of a Nitrogen-Vacancy (NV) center in diamond.
Performance Metrics: Achieved an average storage fidelity of 98%.
Long-Term Memory: Demonstrated an ultra-long nuclear spin coherence time ($\text{T}_{2n}$) exceeding 10 seconds in the $m_s=0$ electron spin manifold (using a Hahn echo sequence).
Methodology: The protocol relies purely on photon absorption and high-fidelity single-shot electronic spin readout for heralding, circumventing the typically low efficiency (4%) associated with Zero Phonon Line (ZPL) emission approaches.
Stability for Repeaters: The nuclear spin memory exhibits robustness, supporting over 5000 iterations of optical writing operations (60 µs coherence time under continuous illumination), essential for quantum repeater node functionality.
Future Utility: This architecture paves the way for absorption-based quantum repeater networks and enables the potential generation of multi-photon entangled states (e.g., 10-photon GHZ states at 1 Hz rate).
Material Implication: Success hinges on using high-purity, low-strain single crystal diamond, underscoring the necessity of high-specification MPCVD materials.

Technical Specifications

Parameter	Value	Unit	Context
Photon Storage Fidelity	98	%	Average fidelity of transfer to nuclear spin.
Nuclear Spin $\text{T}_{2n}$ (Hahn Echo, $m_s=0$)	> 10	seconds	Coherence time measurement essential for memory lifespan.
Nuclear Spin $\text{T}_{2n}$ (Ramsey, $m_s=0$)	0.31 ± 0.05	seconds	Decoherence limit set by the surrounding ¹³C bath noise.
Minimum Operating Temperature (T)	< 8	K	Required for resonant optical excitation and efficient initialization/readout.
Optical Writing Pulse Width	12	ns	Matched to the excited state lifetime.
Electronic Excited State Lifetime	12	ns	Spontaneous emission time.
NV Strain Splitting (Targeted)	≈ 1.2	GHz	Low strain selected to suppress unwanted excited state configuration mixing.
Optical Rabi Frequency	27	MHz	Corresponding to 200 nW laser power during writing.
Repetitive Writing Stability	5000	rounds	Achieved under continuous illumination, limited by 60 µs coherence time.
Required Photon Wavelength	637	nm	Wavelength required for connecting adjacent quantum nodes (NV center ZPL).

Key Methodologies

The quantum storage protocol is realized through four synchronized steps executed on a low-strain NV center in diamond at cryogenic temperatures (T < 8 K).

High-Fidelity Nuclear Spin Initialization:
- The ¹⁴N nuclear spin is deterministically initialized into the $\text{|0}\rangle_n$ state with > 98% fidelity.
- This is achieved via polarization transfer from the electron spin using a nuclear-spin-controlled NOT gate sequence, starting from the electron spin $\text{|0}\rangle_e$.
Electron-Nuclear Bell State Preparation:
- The hybrid system is prepared in the initial Bell state $\text{|\Psi}^{+}\rangle$ from the $\text{|0}\rangle_e \text{|0}\rangle_n$ state using a nuclear $\pi$ pulse followed by a nuclear-spin-controlled NOT gate.
Photon Absorption (Writing):
- A polarization-encoded photon is sent resonant with the $\text{|A}_{1}\rangle$ transition, coherently exciting the electron spin from the ground state $\text{|\pm 1}\rangle_e$.
- The absorption process transfers the photon state into an entangled electron-nuclear spin state, synchronized to occur within 20 ns of Bell state preparation to minimize decoherence.
Heralding and Readout:
- Heralding: Successful absorption and storage are confirmed by a single-shot readout of the electronic spin state $\text{|0}\rangle_e$ after rapid relaxation.
- Nuclear Readout: The stored phase information is mapped onto the nuclear spin population via an RF pulse. Electron spin Rabi oscillations, conditioned on the nuclear spin states, are then measured to reconstruct the final density matrix and determine the storage fidelity.

6CCVD Solutions & Capabilities

6CCVD provides the specialized MPCVD diamond materials and precision engineering services necessary to replicate and advance this cutting-edge research in solid-state quantum memory and quantum networking.

Applicable Materials

The key to achieving ultra-long coherence times (T_2n > 10s) and supporting scalable repeater functionality is material purity and isotopic control, which minimizes the surrounding spin bath noise ($\text{}^{13}\text{C}$ concentration).

Material Grade	Description & Requirement Alignment	Technical Specifications Offered
Optical Grade Single Crystal Diamond (SCD)	Required for high-fidelity resonant optical excitation (637 nm ZPL). The material must exhibit low background strain and minimal defect density to host low-strain NV centers (≈1.2 GHz strain splitting).	Thickness: 0.1 µm to 500 µm (Custom SCD epitaxial layers). Polishing: $\text{R}_{a} \lt 1 \text{ nm}$ for optimal optical interface.
Isotopically Enriched ¹²C SCD	Crucial for maximizing T_2n. The paper explicitly recommends ¹²C enrichment to suppress the natural ¹³C nuclear spin bath, which limits electron spin T₁ and is the primary source of nuclear spin decoherence in the $m_s=0$ manifold.	Isotopic Purity: Available up to 99.999% ¹²C concentration, tailored to experimental requirements for extending coherence times well beyond 10 seconds.
Custom Substrates	Enables replication of the low-strain environment and proper orientation.	SCD wafers/plates available up to 125 mm diameter; custom laser micro-machining for integration into cryostat systems (e.g., precision alignment of [111] NV centers).

Customization Potential

The integration of NV centers into a functional quantum network requires precision engineering of the diamond chip for electronic control and photonic coupling.

Custom Dimensions: 6CCVD provides precision laser cutting and micro-shaping of SCD plates to unique dimensions required for integration into microwave resonators or photonic structures, ensuring alignment with the [111] orientation used in the study.
Integrated Metalization: To enable the necessary MW/RF control pulses (e.g., $\pi$ pulses and nuclear-spin-controlled NOT gates) utilized in this protocol, 6CCVD offers internal, in-house thin-film metalization services. We apply high-quality layers of Au, Pt, Pd, Ti, W, or Cu necessary for fabricating electrodes and microwave striplines directly onto the diamond surface.

Engineering Support & Logistics

6CCVD is committed to accelerating quantum research by providing comprehensive support from material selection through final delivery.

Engineering Support: The paper identifies material limitations (strain, ¹³C bath noise, and nitrogen concentration) as key barriers to extending coherence and stability. 6CCVD’s in-house PhD material science team can assist customers with material selection and custom growth recipes to optimize SCD purity and defect density for similar solid-state quantum repeater or entangled photon source projects.
Global Supply Chain: We offer global shipping (DDU default, DDP available) to ensure reliable, timely delivery of critical SCD substrates to research institutions worldwide, minimizing logistical delays for time-sensitive quantum experiments.

Call to Action

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

Tech Support

Original Source

DOI: https://doi.org/10.1038/nphoton.2016.103