Observation of a Quantum Phase from Classical Rotation of a Single Spin

At a Glance

Metadata	Details
Publication Date	2020-01-17
Journal	Physical Review Letters
Authors	A. A. Wood, Lloyd C. L. Hollenberg, R. E. Scholten, A. Martin
Institutions	Centre for Quantum Computation and Communication Technology, The University of Melbourne
Citations	26
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Speed Quantum Rotation Sensing using NV Centers

This document analyzes the requirements and achievements detailed in the research paper “Observation of a quantum phase from classical rotation of a single spin” and maps them directly to 6CCVD’s advanced MPCVD diamond capabilities, positioning our materials as the optimal choice for replicating and extending this cutting-edge quantum sensing research.

Executive Summary

The research successfully demonstrates the observation of a quantum phase shift induced by the classical physical rotation of a single Nitrogen-Vacancy (NV) electron spin in diamond. This achievement validates the use of NV centers as robust, room-temperature quantum gyroscopic sensors.

Core Achievement: Direct measurement of a rotationally-induced phase shift ($\delta\phi$) in a single NV qubit using spin-echo interferometry.
High-Speed Operation: The experiment was conducted on a high-purity diamond rotating at an extreme rate of 200,000 rpm (3.33 kHz).
Key Methodology: Utilizing the nonlinear accumulation of the effective phase ($\phi_{eff}$) due to the interaction between the rotating NV axis and a tilted microwave field ($\theta_{mw} \neq 0$).
Material Requirement: The success relies critically on isotopically enriched 99.99% ¹²C Single Crystal Diamond (SCD) to achieve long coherence times ($T_{2}$ up to 1 ms) necessary for extended interferometric interrogation.
6CCVD Value Proposition: 6CCVD provides the necessary ultra-high purity, low-strain SCD substrates with custom isotopic enrichment and precise crystallographic orientation ((100) used here) required for next-generation quantum rotation sensors.

Technical Specifications

The following hard data points were extracted from the experimental setup and results:

Parameter	Value	Unit	Context
Diamond Purity	99.99% ¹²C	%	Isotopic enrichment for long $T_{2}$
Rotation Rate	200,000	rpm	Physical rotation speed of the diamond
Rotation Frequency ($\omega_{rot}$)	3.33	kHz	Equivalent rotation frequency
NV Center Location	~3	µm	Distance from the rotation axis
NV Axis Tilt ($\theta_{NV}$)	54.7	°	Angle relative to the rotation axis (z)
Zero-Field Splitting ($D_{zfs}$)	2.870	GHz	Intrinsic NV property
Microwave Frequency ($\omega$)	2.846	GHz	Near-resonant driving field
Coherence Time ($T_{2}$)	$\approx 50$	µs	Typical measured coherence time
Coherence Time ($T_{2}^{*}$)	$\approx 1$	ms	Maximum measured coherence time
Spin-Echo Interrogation Time ($\tau$)	100	µs	Duration of the interferometric sequence
Microwave Tilt Angle ($\theta_{mw}$) Range	28 to 67	°	Varied by wire position

Key Methodologies

The experiment utilized a highly controlled setup combining high-speed mechanical rotation with precise microwave and optical control over the NV spin state.

Material Preparation: A high-purity, isotopically enriched (100)-oriented ¹²C diamond hosting individually resolvable NV centers was used.
Mechanical Setup: The diamond was mounted on its (100) face to an electric motor rotating about the z-axis at 3.33 kHz (200,000 rpm).
Optical Pumping: NV spins were initialized and read out using 532 nm laser light, with fluorescence collected in the 600-800 nm range.
Microwave Control: Microwaves (2.846 GHz) were applied via a 20 µm diameter copper wire positioned above the diamond surface. The position of this wire was translated to vary the microwave tilt angle ($\theta_{mw}$).
Synchronization: Single NV centers were imaged using a scanning confocal microscope with illumination pulsed synchronously with the motor rotation.
Interferometric Sequence: A pulsed spin-echo sequence ($\pi/2 - \tau/2 - \pi - \tau/2 - \pi/2$) was applied. The sequence was synchronized to the rotation period, and a delay time was used to change the starting angle ($\phi_0$).
Phase Extraction: The rotationally-induced phase shift ($\delta\phi$) was extracted by fitting the resulting spin-echo interference fringes, which were traced out as a function of an applied DC magnetic field ($B_x$).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the specialized diamond materials and processing required to replicate, optimize, and scale this research into practical quantum rotation sensors.

Applicable Materials

To achieve the long coherence times ($T_{2}$ up to 1 ms) and low-strain environment necessary for sensitive interferometry, the following 6CCVD materials are required:

6CCVD Material	Specification	Relevance to Research
Optical Grade SCD	Ultra-low nitrogen content (< 1 ppb)	Minimizes background defects and strain, maximizing $T_{2}$.
Isotopically Purified SCD	99.99% ¹²C enrichment	Essential for decoupling the NV spin from the nuclear spin bath, achieving the reported long $T_{2}$ times.
Custom Orientation	(100) or (111) orientation	The paper used (100) mounting; 6CCVD provides precise crystal orientation control for optimal NV alignment relative to the rotation axis.

Customization Potential

The experimental setup utilized a 20 µm external copper wire for microwave delivery. 6CCVD offers integrated solutions that simplify the setup and improve RF coupling efficiency:

Custom Dimensions: We provide plates and wafers up to 125 mm (PCD) and SCD substrates up to 10 mm thick. For high-speed rotation experiments, we can supply custom-cut, thin SCD wafers (0.1 µm to 500 µm thickness) with precise edge finishing to minimize rotational instability.
Integrated Metalization: 6CCVD offers in-house deposition of thin-film metal layers directly onto the diamond surface.
- Recommended Metal Stack: Ti/Pt/Au or Ti/W/Cu for robust, low-loss microwave transmission lines (e.g., coplanar waveguides or microstrip lines) to replace the external copper wire.
- Benefit: Integrated metalization ensures precise, fixed microwave tilt angles ($\theta_{mw}$) and eliminates mechanical instability associated with external wiring during high-speed rotation.
Advanced Polishing: We guarantee ultra-smooth surfaces, critical for minimizing scattering losses during optical pumping and readout.
- SCD Polishing: Surface roughness $R_a < 1$ nm.

Engineering Support

6CCVD’s in-house PhD team specializes in optimizing MPCVD diamond for quantum applications. We offer consultation services to researchers working on similar Quantum Gyroscopic Sensing and High-Speed Rotation Detection projects.

Material Selection: Assistance in selecting the optimal isotopic purity, crystal orientation, and thickness for maximizing NV coherence and minimizing rotational strain effects.
NV Creation Protocols: Guidance on post-growth processing (e.g., irradiation and annealing) to achieve high-density, shallow, or specific NV ensembles required for advanced sensing schemes.

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

View Original Abstract

The theory of angular momentum connects physical rotations and quantum spins together at a fundamental level. Physical rotation of a quantum system will therefore affect fundamental quantum operations, such as spin rotations in projective Hilbert space, but these effects are subtle and experimentally challenging to observe due to the fragility of quantum coherence. We report on a measurement of a single-electron-spin phase shift arising directly from physical rotation, without transduction through magnetic fields or ancillary spins. This phase shift is observed by measuring the phase difference between a microwave driving field and a rotating two-level electron spin system, and it can accumulate nonlinearly in time. We detect the nonlinear phase using spin-echo interferometry of a single nitrogen-vacancy qubit in a diamond rotating at 200 000 rpm. Our measurements demonstrate the fundamental connections between spin, physical rotation, and quantum phase, and they will be applicable in schemes where the rotational degree of freedom of a quantum system is not fixed, such as spin-based rotation sensors and trapped nanoparticles containing spins.

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevlett.124.020401