Bulk Diamond NV Center Sensing via Light-Trapping Geometry
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Solution Overview
Problem
Current methods for sensing quantum mechanical spin states in diamond crystals face limitations in efficiently exciting and collecting signals from large ensembles of nitrogen vacancy (NV) centers due to low absorption cross-sections and coherence time constraints, which restrict the sensitivity and resolution of quantum sensing applications.
Innovation Solution
A method and apparatus that utilize a room-temperature bulk crystalline material, such as diamond, with a plurality of color centers, where an electromagnetic beam is coupled into the material through a propagation path with multiple reflections to excite the color centers, and the quantum mechanical spin states are determined from detected electromagnetic radiation, allowing for the measurement of strain, temperature, and electromagnetic fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional single-pass excitation methods are used, then the setup is simple, but the number of NV centers interacting with the laser beam is limited due to low absorption cross-sections
Solution Approach 1:
The patent transforms the single-pass linear excitation path into a multi-dimensional zigzag propagation path by utilizing total internal reflections at multiple surfaces of the bulk crystal. This dimensional transformation allows the laser beam to interact with NV centers throughout the entire volume of the crystal rather than being limited to a single traversal path, thereby dramatically increasing the effective number of interacting NV centers.
Solution Approach 2:
The patent introduces the crystal surfaces as intermediary elements that facilitate multiple interactions between the laser beam and NV centers. By utilizing total internal reflection at these surfaces, the system creates an extended interaction path without requiring additional external components, allowing the beam to bounce through the crystal volume and excite numerous NV centers that would otherwise remain inaccessible.
2Measurement precision
If the laser beam path is extended to excite more NV centers, then sensing sensitivity improves, but signal collection efficiency decreases
Solution Approach 1:
The patent merges the excitation function and the signal collection function into a single integrated optical path. The same zigzag trajectory that enables extended excitation of NV centers also serves as the collection path for detecting their spin state signals. This merging ensures that photons emitted by NV centers deep within the crystal can be efficiently collected by the detector without requiring separate optical paths, thereby maintaining high signal collection efficiency while achieving high sensing sensitivity.
3Length of stationary object
If multiple reflections are used to excite more NV centers, then the interaction path increases, but maintaining long spin coherence times becomes more difficult
Solution Approach 1:
The patent utilizes the intrinsic optical properties of the bulk crystal itself to achieve multiple reflections and extend the optical path length. By designing the crystal geometry and utilizing total internal reflection at its surfaces, the system creates a self-contained zigzag propagation path that does not require external mirrors or reflective coatings. This self-service approach minimizes additional interaction points that could introduce decoherence, thereby maintaining long spin coherence times while achieving extended NV center excitation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the sensitivity and resolution of quantum sensing by increasing the number of NV centers interacting with the laser beam, achieving efficient excitation and collection of signals, and maintaining long spin coherence times, thereby improving the performance in applications like magnetometry, thermometry, and pressure sensing.
Implementation Method 1
The propagation path includes a plurality of reflections off surfaces of the room-temperature bulk crystalline material so as to cause the electromagnetic beam to excite the color centers
Implementation Method 2
detecting, with at least one detector, electromagnetic radiation emitted and/or transmitted by the color centers in response to the excitation of the color centers
Data Source
AI summary
A light-trapping geometry enhances the sensitivity of strain, temperature, and/or electromagnetic field measurements using nitrogen vacancies in bulk diamond, which have exterior dimensions on the order of millimeters. In an example light-trapping geometry, a laser beam enters the bulk diamond, which may be at room temperature, through a facet or notch. The beam propagates along a path inside the bulk diamond that includes many total internal reflections off the diamond's surfaces. The NVs inside the bulk diamonds absorb the beam as it propagates. Photodetectors measure the transmitted beam or fluorescence emitted by the NVs. The resulting transmission or emission spectrum represents the NVs' quantum mechanical states, which in turn vary with temperature, magnetic field strength, electric field strength, strain/pressure, etc.