Optical manipulation of the Berry phase in a solid-state spin qubit

At a Glance

Metadata	Details
Publication Date	2016-02-15
Journal	Nature Photonics
Authors	Christopher G. Yale, F. Joseph Heremans, Brian B. Zhou, Adrian Auer, Guido Burkard
Institutions	University of California, Santa Barbara, University of Konstanz
Citations	110
Analysis	Full AI Review Included

Technical Documentation: All-Optical Geometric Phase Control in Solid-State Qubits (NV Diamond)

This technical analysis of the research paper details the demonstration of an all-optical method for accumulating the Berry phase in a nitrogen-vacancy (NV) center in diamond, utilizing Stimulated Raman Adiabatic Passage (STIRAP). This breakthrough enables high-resolution, robust geometric control over solid-state qubits, positioning MPCVD diamond as the foundational material for next-generation photonic quantum networks.

Executive Summary

The paper demonstrates a critical advancement for solid-state quantum computation by replacing traditional microwave control with a robust, all-optical technique for geometric phase manipulation.

All-Optical Geometric Control: Demonstrated the accumulation of the Berry phase ($\gamma_B$) in an individual NV center using diffraction-limited resonant laser fields via STIRAP, offering superior spatial resolution compared to traditional microwave methods.
Enhanced Speed: Achieved adiabatic interaction times as short as $\tau \sim 250$ ns, enabled by high optical Rabi frequencies ($\Omega_R$ up to 64 MHz). This represents a 100-fold speedup over previous atomic demonstrations.
Noise Robustness Confirmed: Geometric control showed strong resilience to parallel noise ($\delta\theta$) and intrinsic noise resilience scales as $\sigma_{\gamma B} \sim \tau^{-1/2}$, confirming the fault-tolerant nature of geometric quantum gates.
High Qubit Fidelity: Experimental Berry phase visibility peaked at 51%, corresponding to an estimated peak state fidelity of 73%.
Integrated Platform: The experiment used an electronic grade Single Crystal Diamond (SCD) substrate requiring integrated metalized waveguides (Ti:Au stack) for on-chip microwave preparation and tomography.
Future Photonic Networks: This technique establishes the foundation for independent manipulation of solid-state qubits within integrated photonic networks and larger spin arrays.

Technical Specifications

The following hard parameters define the experimental conditions and performance metrics achieved using the NV center in the diamond substrate.

Parameter	Value	Unit	Context
Material Used	Electronic Grade Diamond	N/A	Substrate source for NV centers
Substrate Dimensions	2 x 2 x 0.5	mm	Sample size used in the cryostat
Operating Temperature	8	K	Liquid helium flow cryostat environment
External Magnetic Field	117	G	Applied along the NV center axis
Zeeman Splitting	655	MHz	Split $\vert -1_g \rangle$ and $\vert +1_g \rangle$ ground states
STIRAP Laser Wavelength	637	nm (470 THz)	Resonant drive frequency
Maximum Optical $\Omega_R$	64	MHz	Rabi Frequency achieved for fastest adiabatic evolution
Minimum Traversal Time ($\tau$)	250	ns	Achieved at $\Omega_R = 64$ MHz
Required Two-Photon Detuning ($\delta$) Precision	< 150	kHz	Required to minimize dynamic phase uncertainty
Peak State Fidelity	73	%	Estimated from maximum observed Berry phase visibility
Waveguide Metalization Stack	Ti (10 nm) / Au (100 nm)	nm	Short-terminated on-chip microwave control
Intrinsic Noise Resilience	$\sigma_{\gamma B} \sim \tau^{-1/2}$	N/A	Observed scaling for geometric phase robustness

Key Methodologies

The experiment relies on high-purity material and sophisticated integration of optical and microwave components for precise quantum control.

Diamond Substrate Preparation: Utilization of a 2 x 2 x 0.5 mm electronic grade Single Crystal Diamond (SCD) substrate containing naturally formed, negatively charged NV centers.
Microwave Integration: Lithographic patterning of Ti (10 nm) / Au (100 nm) short-terminated waveguides onto the diamond surface to enable on-chip microwave (MW) control for spin preparation and tomographic projection.
Environmental Setup: Sample is thermally sunk within a liquid helium flow cryostat, maintaining a stable temperature of T = 8 K. An external 117 G magnetic field is applied to tune the $\vert -1_g \rangle$ and $\vert +1_g \rangle$ states via the Zeeman effect (655 MHz splitting).
Optical Field Generation: A tunable 637 nm laser beam is coupled through an Electro-Optic Modulator (EOM). Driving the EOM at 655 MHz generates frequency harmonics (sidebands) equivalent to the spin splitting, which are used to drive the $\Lambda$ transitions ($\vert \pm 1_g \rangle$ to $\vert A_2 \rangle$).
Adiabatic Passage Control (STIRAP): A phase quadrature modulator, governed by an Arbitrary Waveform Generator (AWG), controls the relative amplitude ($\Omega_{\pm 1}(t)$) and phase ($\phi(t)$) of the optical fields on nanosecond timescales, guiding the spin along closed loops on the Bloch sphere to enclose the Berry phase ($\gamma_B$).
Phase Measurement: The accumulated phase is measured relative to the $\vert 0_g \rangle$ ground state (used as a reference) by performing state tomography after the STIRAP cycle is complete.
Robustness Analysis: Simulated noise ($\delta\theta$ parallel and $\delta\phi$ perpendicular) was intentionally introduced to control parameters to verify the intrinsic noise resilience of the geometric Berry phase.

6CCVD Solutions & Capabilities

This research highlights the critical need for high-quality, customized diamond materials and advanced processing techniques. 6CCVD is an expert technical partner capable of supplying and engineering the materials required to replicate, scale, and extend this critical quantum research.

Material Requirement Mapping for Quantum Photonic Applications

Research Requirement	6CCVD Material Solution	Customization & Engineering Capability
High-Purity NV Host Material	Optical Grade Single Crystal Diamond (SCD)	SCD is available with ultra-low impurity levels, ideal for maximizing NV or Silicon-Vacancy (SiV) coherence times (dephasing rates up to $2.25 \text{ µs}$ observed).
Custom Size and Thickness	Custom Dimensions & Thickness: Plates/wafers up to 125 mm (PCD). SCD and PCD material thicknesses are available from $0.1 \text{ µm}$ to $500 \text{ µm}$. Substrates up to 10 mm.	We can replicate the $2 \text{ x } 2 \text{ x } 0.5 \text{ mm}$ size or provide larger inch-size wafers for scaling qubit arrays (Ref 16).
On-Chip Metalization (Ti:Au)	Integrated Metalization Services: Internal capability for deposition of Au, Pt, Pd, Ti, W, and Cu stacks.	We provide the exact Ti (10 nm) / Au (100 nm) stack required for short-terminated waveguides, ensuring critical low-resistance contacts for high-frequency (655 MHz) MW control.
Surface Quality for Optical Coupling	High-Fidelity Polishing: Achieved surface roughness Ra < 1 nm (SCD) or Ra < 5 nm (Inch-size PCD).	Essential for minimizing optical scattering losses and enabling high Numerical Aperture (NA 0.85) objective focusing, crucial for diffraction-limited spatial resolution.
Next-Generation Qubit Expansion	Boron-Doped Diamond (BDD) and Specialty SCD for SiV/GeV	Provides the material foundation required to transition to promising alternative $\Lambda$ systems like the Silicon-Vacancy (SiV) center (Ref 35-37), which offer strong zero-phonon line emission and better photonics integration.

Engineering Support & Call to Action

The sophisticated optical and microwave control demonstrated in this paper requires meticulous material preparation. 6CCVD’s in-house PhD engineering team specializes in diamond material selection, optimization, and processing integration for solid-state quantum computing and nanophotonics projects. We ensure that critical material properties—such as purity, thickness control, and surface finish—meet the exacting requirements for cryogenic, high-coherence qubit operation.

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.2015.278