Setup

Quantum Diamond Spectrometer (QDS) is a setup for addressing ensembles of NV centers in diamond. Green laser excitation is projected onto bulk diamond, and the fluorescence emission is collected via a hexagonal optical light guide into an avalanche photodiode for photon detection. The setup is adapted from Bucher et. al (Nature Protocols 2019), Quantum Diamond Spectrometer for Nanoscale NMR and ESR Spectroscopy.

From optical alignment, 532-nm laser passes through convex lens f= 100 mm to focus beam in to an acousto-optic modulator (AOM) which create diffraction patterns by Piezo transducer with RF driver. Before the patterns are chosen by diaphragm for turning on/off laser to diamond, the laser is collimated by convex lens f = 150 mm. After that the diffracted laser pass polarizer and half-wave plate to control light polarization. After that, polarized laser is demagnified with 2 convex lens f =200 mm and f = 30 mm by 0.15 times. The collimated beam focus with convex lens f =50 mm to the diamond on top of light guide. The diamond is illuminated by green laser and release red fluorescence through the light guide to the detector. Before the detector receives fluorescence signal, there are 2 filters for blocking green laser and wavelength selection. Finally, the signal is collected by data acquisition to process in computer.

Above the diamond sample, a microwave loop is brought into close proximity to the diamond and a set of permanent magnets is set to tune the NV energy states. Both instruments can be rotated and translated to maximize the setup efficiency.

The setup we have constructed in our lab consists of the following parts:

1. Magnet holder: Two permanent magnets are affixed on a rail where the distance and orientation can be tuned to position along the NV axis in diamond for best ESR contrast.
2. Light guide: This part can set for glue diamond as we must shoot green laser into diamond. The light guide bring light to avalanche photo diode.
3. Detector: It is avalanche photodiode. When red fluorescence emission is collected through the light guide, the detector converts photon energy into analog voltage that can be read from the data acquisition card.

Comparison Between QDS and Single NV Confocal Microscope

Normally, single NV centers are addressed using confocal microscopy [see details]. QDS offers several advantages over single-photon confocal microscopy, albeit with some limitations, which we outline below

Advantages of QDS setup

• Using Ensemble NV: We study quantum phenomenon and quantum controlling. Much signal is important research. So, ensemble NV can support it.
• Easy Alignment: In this setup, QDS be easily adjusted for choosing comfortable angles which bring laser to excite NV and can change microwave loop position for controlling.
• Creativity: Some parts does not match on paper. We must design those for match position.
• QDS give a dimension datum.

Advantage of Single NV Confocal Microscope

• No noise: Normally, Confocal microscope must have a pinhole to remove noise signals. Single NV confocal use filter to select detected signals. So, they have reliability to analyze phenomenon.
• Alignment Practice: Single NV confocal have optical instruments. They must be aligned to pass green laser to diamond with desired diameter light. Alignment is basic skill to practice ourselves for example fiber coupling, change x, y and z axis for bring laser into collimator, is a part to be patiently to precisely adjust.
• Various factor: Single NV confocal can change factors for phenomenon study such as magnetic angle of interaction between NV and magnet, number of magnet and etc.. So, parameters changing can choose good signals for detection.
• Confocal microscope give 2 dimension data(picture).

Limitation of QDS setup

• A lot of signals: Ensemble NV can various signals. Sometimes, they are unnessary and disturb detected-signals peroid.
• No Practices: When alignment is easy, we do not spend time to adjust alignment.

Limitation of Single NV Confocal Microscope

• Time: If we need potential signals, we need to spend time to set precise alignment.
• Discrepancy: Detected Single NV may be move out from detection. It affects to many set parameters. We need find comfortable variables for the setup.

Project