Tolerance in the Ramsey interference of a trapped nanodiamond

At a Glance

Metadata	Details
Publication Date	2016-04-27
Journal	Physical review. A/Physical review, A
Authors	C. C. Wan, M. Scala, Sougato Bose, Angelo Frangeskou, ATM A. Rahman
Institutions	Imperial College London, University College London
Citations	22
Analysis	Full AI Review Included

6CCVD Technical Analysis: Tolerance in the Ramsey Interference of a Trapped Nanodiamond

This document analyzes the technical requirements and experimental constraints presented in the paper Tolerance in the Ramsey interference of a trapped nanodiamond (arXiv:1509.00724v1) and aligns them with the single crystal diamond (SCD) and fabrication capabilities offered by 6CCVD.com.

Executive Summary

This research utilizes an NV center spin in a trapped nanodiamond to detect gravity-induced quantum phase shifts, pushing the boundaries of macroscopic quantum superposition experiments.

Core Application: Demonstrating Ramsey interference and detecting gravitational phase shifts in a mesoscopic quantum system (nanodiamond center of mass).
Methodology: Conditional displacement of a nanodiamond (R ~ 100 nm) trapped in an optical tweezer, coupled to a single Nitrogen-Vacancy (NV) center spin.
Critical Material Requirement: Ultra-high purity, isotopically engineered Single Crystal Diamond (SCD) is essential to achieve the required electron spin coherence time ($T_2 > 79$ µs).
Robustness Confirmation: The analysis proves the scheme is highly robust, maintaining fidelity > 99% despite coupling to unwanted motional degrees of freedom and resisting thermal fluctuations up to 1 mK.
Experimental Feasibility: The necessary physical parameters (e.g., $\omega_z \sim 100$ kHz, magnetic field gradient $\sim 10^{7}$ T/m) are experimentally achievable, simplifying the proof-of-principle experiment.
6CCVD Value: 6CCVD provides the necessary high-quality, isotopically purified SCD precursors for fabricating the required low-defect nanodiamond particles and pillars.

Technical Specifications

Parameter	Value	Unit	Context
Nanodiamond Radius (R)	~100	nm	Target particle size for trapping
Diamond Mass (m)	~1.25 x 10^-17	kg	Calculated mass of the trapped bead
Diamond Density	3500	kg/m³	Standard material constant
Axial Trapping Frequency ($\omega_z$/2$\pi$)	~100	kHz	Realistic experimental trapping frequency
Required Spin Coherence Time ($T_2$)	> 79	µs	Minimum time needed for high fringe visibility
Maximum Thermal Robustness	1	mK	Temperature limit for robust results (avoids anharmonic effects)
Required Magnetic Gradient	~10⁷	T/m	Gradient necessary for spin-motion coupling (dB/dz)
System Fidelity (Perturbative)	> 99	%	Fidelity maintained between realistic and 1D model
Trap Laser Wavelength	1064	nm	Wavelength used for optical tweezer

Key Methodologies

The experiment relies on precision CVD diamond materials and advanced quantum control techniques:

Material Selection: Use of nanodiamond containing a single S=1 NV center. High-purity, isotopically enriched diamond is required (low nitrogen, ¹³C depletion) to maximize the electron spin $T_2$ coherence time.
Nanofabrication: Fabrication of nanodiamonds (or specifically, nanodiamond pillars down to 50 nm diameter / 150 nm length) typically achieved via processes like milling or Reactive Ion Etching (RIE) on bulk SCD precursors.
Optical Trapping: Levitating the nanodiamond bead in ultra-high vacuum using a tightly focused 1064 nm laser dipole trap (optical tweezer).
Spin-Motion Coupling: Inducing conditional displacement via the interaction between the NV center’s magnetic moment and a static magnetic field gradient ($\sim 10^{7}$ T/m).
Ramsey Interferometry: Applying a sequence of microwave pulses to the NV spin to prepare a superposition state, allow gravity-induced phase accumulation ($t_0 \approx 50$ µs), and read out the resulting phase shift from the spin state population $P_0$.

6CCVD Solutions & Capabilities

Replicating and extending this foundational quantum mechanics research requires diamond materials with specific purity, dimensional precision, and defect engineering characteristics—areas where 6CCVD provides world-leading capabilities.

Applicable Materials

The long coherence times ($T_2$) required (79 µs minimum, ideally longer) are dependent on minimizing decoherence sources, specifically nitrogen and ¹³C impurities.

Recommended Material: High Purity Optical Grade Single Crystal Diamond (SCD)
- Purity Specification: Ultra-low nitrogen content ([N] < 1 ppb) to maximize $T_2$.
- Isotopic Engineering: ¹³C depletion (< 1%) via controlled methane gas precursors during CVD growth to suppress magnetic noise and ensure coherence sufficient for multi-cycle phase accumulation.

Customization Potential

The experimental preparation requires high-quality precursors for nanofabrication (RIE/Milling) and specific geometry for integration into the optical setup.

Requirement from Paper	6CCVD Capability	Benefits for Researchers
Precursor Plates for RIE/Milling (Nanodiamonds/Pillars)	SCD plates available up to 500 µm thick, and thick substrates up to 10 mm.	Provides necessary bulk material thickness and quality for precision top-down fabrication of required nanostructures (50-100 nm scale).
Dimensional Flexibility	Custom dimensions for plates and wafers up to 125 mm (PCD/SCD upon request).	We can provide precise, laser-cut precursor sizes optimized for subsequent nanofabrication processes.
Surface Quality	SCD Polishing to Ra < 1 nm.	Minimizes surface defects which could act as spurious pinning centers or introduce unwanted decoherence during trapping.
Integration Interfaces (If needed for complex setups)	Custom metalization services: Au, Pt, Pd, Ti, W, Cu.	Allows researchers to integrate electrode structures or bonding pads directly onto the diamond platform for magnetic control or trapping optimization.

Engineering Support

6CCVD acts as a technical partner, leveraging deep expertise in CVD material science to accelerate quantum research.

Material Optimization: Our in-house PhD material science team can assist researchers in selecting the optimal SCD orientation, nitrogen concentration, and isotopic ratio required to maximize $T_2$ coherence for complex [Trapped Nanodiamond Interferometry] projects.
Specification Consultation: We offer consultation to ensure that the material thickness and dimensions provided are perfectly suited as precursors for post-growth fabrication methods like RIE or focused ion beam milling, crucial for achieving the required 100 nm-scale particles/pillars.

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

View Original Abstract

In the scheme recently proposed by M. Scala et al. [Phys. Rev. Lett. 111, 180403 (2013)], a gravity-dependent phase shift is induced on the spin of a nitrogen-vacancy (NV) center in a trapped nanodiamond by the interaction between its magnetic moment and the quantized motion of the particle. This provides a way to detect spatial quantum superpositions by means of only spin measurements. Here, the effect of unwanted coupling with other motional degrees of freedom is considered, and we show that it does not affect the validity of the scheme. Both this coupling and the additional error source due to misalignment between the quantization axis of the NV center spin and the trapping axis are shown not to change the qualitative behavior of the system, so that a proof-of-principle experiment can be neatly performed. Our analysis, which shows that the scheme retains the important features of not requiring ground-state cooling and of being resistant to thermal fluctuations, can be useful for several schemes which have been proposed recently for testing macroscopic superpositions in trapped microsystems.