Experimental investigation of quantum entropic uncertainty relations for multiple measurements in pure diamond

At a Glance

Metadata	Details
Publication Date	2017-05-24
Journal	Scientific Reports
Authors	Jian Xing, Yu-Ran Zhang, Shang Liu, Yanchun Chang, Jie-Dong Yue
Institutions	Chinese Academy of Sciences, University of Chinese Academy of Sciences
Citations	19
Analysis	Full AI Review Included

Experimental Investigation of Quantum Entropic Uncertainty Relations in Diamond: Technical Documentation

This document summarizes the key findings and methodologies of the research paper “Experimental investigation of quantum entropic uncertainty relations for multiple measurements in pure diamond,” and demonstrates how 6CCVD’s advanced CVD diamond capabilities are essential for replicating and scaling this foundational quantum research.

Executive Summary

Core Achievement: First room-temperature experimental testing and confirmation of entropic uncertainty relations (EUR) for multiple (three) measurements in a natural, three-dimensional solid-state system.
System Used: The electron spin of a single Nitrogen-Vacancy (NV) center embedded in high-purity diamond single crystal (SCD).
Significance: Demonstrates a more precise description of the fundamental uncertainty principle applicable to higher-dimensional quantum states, overcoming limitations found in qubit systems or those requiring quantum memory.
Operating Conditions: Crucially, all experiments were conducted successfully at room temperature, enhancing the feasibility for practical quantum device implementation.
Technical Methodology: Quantum states were prepared and manipulated using precise microwave (MW) pulse sequences (Rabi oscillations in the nanosecond range) combined with Optically Detected Magnetic Resonance (ODMR) for high-fidelity readout.
Material Requirements: Success relies on ultra-high purity diamond with low background nitrogen concentration (< 5 ppm) to maximize electron spin coherence time (T₂*).
Future Impact: This research paves the way for advanced solid-state quantum cryptography, nonlocality tests, and fundamental investigations into quantum thermodynamics.

Technical Specifications

The following hard data points detail the physical parameters and experimental outcomes of the quantum uncertainty relation measurements:

Parameter	Value	Unit	Context
Quantum System	NV Center Electron Spin	N/A	Three-level system (m_s=0, m_s=±1)
Operating Environment	Solid State	N/A	Room temperature operation
Zero-Field Splitting ($D$)	2.87	GHz	Ground state electron spin resonance frequency
Excitation Wavelength	532	nm	Laser source for initialization and readout (ODMR)
Nitrogen Impurity Concentration	< 5	ppm	Requirement for the pure diamond crystal
Electron Spin Coherence Time ($T_{2}*$)	~600	µs	Typical value cited for this material grade
Rabi Oscillation Control Window	0 - 400	ns	Range of microwave pulse durations used for manipulation
Electron Spin Readout Fidelity	95.35	%	Fidelity achieved for initial state projection measurement
Entropic Sum Observed (State $	0\rangle$)	~1.30 - 1.60	bits
Entropic Sum Observed (State $	-1\rangle$)	~0.75 - 1.00	bits

Key Methodologies

The experiment utilized high-precision optical and microwave techniques to control and measure the three-dimensional quantum state of the NV electron spin:

Diamond Material Selection: Use of pure single crystal diamond with extremely low nitrogen concentration (< 5 ppm) to ensure isolated NV centers and minimize environmental decoherence.
Optical Initialization: Electron spin state initialized into the $m_{s}=0$ state using a 532 nm laser pulse focused via a scanning confocal microscope setup.
Spin State Preparation: Superposition states (e.g., $(\frac{1}{\sqrt{3}})(|0\rangle + |-1\rangle + |+1\rangle)$) were generated using controlled microwave (MW) pulses tailored in length and phase (e.g., MW${0}$ 26 ns and MW${2}$ 26 ns pulses) to drive Rabi oscillations.
Microwave Control Pulse Sequences: Four independent MW channels (MW${0}$, MW${1}$, MW${2}$, MW${3}$) were used to apply Rabi oscillations (up to 400 ns duration) to execute population reversal and projection schemes (Tables 1 & 2 in the paper).
Projection Measurement: Entropic uncertainty was measured by projecting the initialized state onto three specific sets of eigenvectors ($M_{1}, M_{2}, M_{3}$) using sequences of MW pulses.
Readout (ODMR): The projected results were read out optically by monitoring the change in fluorescence intensity (ODMR signal) using a Single Photon Counting Meter (SPCM), achieving high readout fidelity.

6CCVD Solutions & Capabilities

The successful replication and extension of this high-impact quantum research rely critically on the quality and customization of the diamond substrate. 6CCVD is uniquely positioned to supply the materials necessary to advance solid-state quantum systems.

Applicable Materials

Research Requirement	6CCVD Material Solution	Technical Benefit
Foundation Substrate (Pure Diamond Single Crystal)	Optical Grade Single Crystal Diamond (SCD)	SCD provides the ultra-low-defect lattice required to minimize decoherence and sustain long electron spin coherence times ($T_{2}* \approx 600$ µs).
Purity and Defect Control	High-Purity MPCVD SCD	Our stringent MPCVD growth controls allow for nitrogen concentrations significantly below the < 5 ppm used in the reported experiment, enabling optimization of isolated NV centers and improving fidelity.
High-Density Integration / Scaling	Polycrystalline Diamond (PCD) or Large Area SCD Substrates	6CCVD offers PCD wafers up to 125 mm diameter and large-format SCD, critical for transitioning from single-NV experiments to integrated multi-qubit arrays.

Customization Potential

Replicating and scaling this experiment requires precision engineering beyond standard commercial wafers. 6CCVD directly supports these needs:

Custom Dimensions: We supply SCD plates/wafers with custom dimensions and thickness, ranging from 0.1 µm up to 500 µm for thin-film applications, or robust substrates up to 10 mm for bulk optics and high-power laser applications (e.g., 532 nm laser path used in the experiment).
Surface Quality: The optical readout setup (scanning confocal microscope, 532 nm laser) requires pristine surfaces. 6CCVD provides state-of-the-art SCD polishing, achieving surface roughness Ra < 1 nm, which is essential for maximizing optical coupling efficiency (especially if Solid Immersion Lenses, SILs, are fabricated on the surface).
Metalization Services: While the current paper used external microwave sources, future integration often requires integrated coplanar waveguides. 6CCVD offers internal metalization capability (e.g., Ti/Pt/Au, Cu, W) directly on the diamond surface, streamlining fabrication of quantum control circuitry.

Engineering Support

6CCVD’s in-house team of PhD material scientists understands the fundamental link between diamond material properties and quantum performance metrics (like $T_{2}$ and readout fidelity). We offer comprehensive consultation for projects focused on similar solid-state quantum information and sensing applications. We can advise on:

Optimal NV formation methods (as-grown vs. implantation/annealing).
Isotopic purification (e.g., $99.99%$ ¹²C) to further suppress nuclear spin noise and extend electron spin coherence.
Specific substrate orientations and dimensions to maximize yield in microfabrication processes.

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/s41598-017-02424-6