Quantum-assisted distortion-free audio signal sensing

At a Glance

Metadata	Details
Publication Date	2022-08-08
Journal	Nature Communications
Authors	Chen Zhang, Durga Dasari, Matthias Widmann, Jonas Meinel, Vadim Vorobyov
Institutions	Tokyo Gas (Japan), University of Stuttgart
Citations	12
Analysis	Full AI Review Included

Quantum-Assisted Distortion-Free Sensing: 6CCVD Technical Analysis

Executive Summary

This research demonstrates a novel quantum sensing protocol using Nitrogen-Vacancy (NV) centers in diamond, achieving high fidelity and extended dynamic range for audio signal detection.

Core Achievement: Successful implementation of Quantum Phase-Sensitive Detection (QPSD) combined with heterodyne readout, overcoming the trade-offs between sensitivity, dynamic range, and frequency resolution inherent in conventional quantum metrology.
Extended Dynamic Range: The QPSD protocol achieved a Linear Dynamic Range (LDR) of 96.5 dB for AC magnetic field sensing, significantly exceeding standard interferometric methods.
Material Platform: The experiment relied on high-quality, 99.97% ¹²C enriched Single Crystal Diamond (SCD) ensembles, achieving a long decoherence time of T₂ = 200 µs.
Application Demonstration: Distortion-free reconstruction of arbitrary audio signals (melody and speech) encoded on a 10-20 kHz carrier frequency, demonstrating potential for quantum-assisted telecommunication.
Methodology: Utilizes two synchronized Microwave (MW) driving fields with a frequency offset to achieve rotating frame modulation and lock-in detection of the quantum phase.
Sensitivity: Calibrated QPSD readout sensitivity reached 38 pT/√Hz, confirming high-sensitive measurement capability.

Technical Specifications

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

Parameter	Value	Unit	Context
Sensor Material Type	¹²C enriched SCD	N/A	(111)-oriented, 0.5 mm³ cube
SCD Purity	99.97% ¹²C	N/A	Isotopic enrichment for T₂ maximization
Final NV Concentration	0.4	ppm	After electron irradiation and annealing
Decoherence Time (T₂)	200	µs	Measured using Hahn-echo sequence
Dephasing Time (T₂*)	8.5	µs	Measured using Ramsey sequence
QPSD Magnetic Field Sensitivity	38	pT/√Hz	Calibrated readout sensitivity
Fluorescence Readout Sensitivity	26	pT/√Hz	Conventional readout sensitivity
Linear Dynamic Range (LDR)	96.5	dB	Calculated for AC sensing (without phase wrapping)
Applied AC Field Range	0 to 3	µT	Range tested for linearity comparison
Audio Signal Carrier Frequency	10 to 20	kHz	Demonstrated frequency band
Laser Excitation Wavelength	532	nm	Used for NV center polarization and readout
Laser Power (Excitation)	80	mW	Used in the experimental setup

Key Methodologies

The distortion-free sensing was achieved by combining QPSD with frequency offset heterodyne readout, utilizing precise control over the NV spin state.

Material Selection and Preparation: A high-purity, ¹²C enriched, (111)-oriented Single Crystal Diamond (SCD) cube (0.5 mm³) was used. The material was processed via electron irradiation and annealing to achieve a specific NV ensemble concentration (0.4 ppm) optimized for long T₂ coherence.
Quantum Phase-Sensitive Detection (QPSD): The QPSD scheme employs two synchronized Microwave (MW) driving fields (MW1 and MW2) with a frequency offset (δf). This creates a rotating frame modulation, allowing the quantum phase accumulated by the spin-field interaction to be extracted via demodulation.
Heterodyne Readout: The QPSD technique was integrated with Hahn-echo or CPMG-2 sequences. By setting the measurement sampling time (T_seq = mT_ø), the protocol generates a frequency offset heterodyne signal, resolving the frequency of the detected AC signal.
Signal Acquisition and Demodulation: The NV fluorescence signal was collected and subjected to a two-stage demodulation process using a Lock-In Amplifier (LIA). The first stage demodulates at the sampling frequency (f_s = 1/(2T_seq)), and the second stage demodulates at the rotating frame modulation frequency (δf).
Arbitrary Signal Sensing: Arbitrary audio signals were encoded onto a carrier frequency (e.g., 10 kHz) using an Arbitrary Waveform Generator (AWG) and applied via a single round copper test coil near the diamond.

6CCVD Solutions & Capabilities

The successful replication and extension of this high-performance quantum sensing research require specialized diamond materials and precision engineering capabilities, which are core offerings of 6CCVD.

Research Requirement	6CCVD Solution & Value Proposition
High-Coherence SCD Platform	Optical Grade Single Crystal Diamond (SCD): The achievement of T₂ = 200 µs relies on extremely low strain and high purity. 6CCVD supplies high-quality SCD substrates (0.1 µm to 500 µm thick) with guaranteed low defect density, ideal for maximizing NV ensemble coherence times.
Isotopic Control (¹²C Enrichment)	Custom Isotopic Diamond Growth: We offer MPCVD growth of SCD with high ¹²C enrichment (>99.99%). This is critical for minimizing nuclear spin bath decoherence, directly enabling the long T₂ times necessary for high-sensitivity, high-resolution quantum sensing protocols like QPSD.
Custom Geometries & Substrates	Precision Machining and Thick Substrates: The experiment used a 0.5 mm³ cube. 6CCVD provides custom laser cutting and dicing services to achieve precise geometries. We also offer thick diamond substrates (up to 10 mm) for applications requiring enhanced thermal management or larger sensing volumes.
Integrated MW Components	Advanced Metalization Services: The use of a dielectric resonator antenna and test coils suggests the need for integrated microwave circuitry. 6CCVD offers in-house metalization capabilities (Au, Pt, Pd, Ti, W, Cu) for creating high-fidelity contact pads, waveguides, or micro-antennas directly on the diamond surface.
Optimized Optical Readout	Ultra-Low Roughness Polishing (Ra < 1 nm): Our SCD wafers are polished to an industry-leading surface roughness of Ra < 1 nm. This minimizes scattering of the 532 nm excitation laser, ensuring maximum photon collection efficiency and optimizing the fluorescence signal contrast (C), which directly impacts sensor sensitivity.
Scaling and Volume Production	Large Area PCD Wafers (up to 125 mm): For scaling up quantum sensor arrays or flux concentrator integration, 6CCVD can provide large-area Polycrystalline Diamond (PCD) wafers up to 125 mm in diameter, offering cost-effective platforms for ensemble NV magnetometry.

Engineering Support: 6CCVD’s in-house PhD team can assist researchers and engineers in selecting and optimizing diamond material specifications (e.g., NV density, isotopic purity, crystal orientation) required to replicate or extend this distortion-free sensing protocol for advanced quantum radio and telecommunication projects.

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/s41467-022-32150-1