THORLABS EDU-QOP1 - User Manual

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Overview

Function Description
Important Technical Specifications
Usage Features
Maintenance Features

The EDU-QOP1(/M) Quantum Optics Kit is an educational system designed to allow students to investigate the quantum properties of light in an open and accessible environment. It focuses on demonstrating what constitutes a non-classical light source, specifically a heralded single photon source that generates pairs of 810 nm photons from a 405 nm pump laser using a type-I BBO crystal. The kit utilizes free-space optics and small single-photon detectors, enabling students to place detectors within the system and perform measurements at specific points. Modern time-tagging electronics are employed to analyze and correlate signals from three single-photon detectors.

Function Description:

The kit facilitates a range of quantum optics experiments, including:

Characterization of a Photon Pair Source: Students can verify that the BBO crystal generates photon pairs, observing coincidence counts significantly exceeding those expected from arbitrary/thermal light sources.
Proof of Non-Classical Light (Grangier-Roger-Aspect Experiment): This experiment demonstrates that when both photons of a pair are considered, the light in one arm exhibits non-classical properties, acting as a heralded single photon source.
Falsification of Attenuated Lasers as Single Photon Sources: Students can experimentally confirm that even a strongly attenuated laser does not behave as a single photon source, as its photon statistics remain classical (Poissonian distribution).
Single Photon Interference in a Michelson Interferometer: This experiment allows students to observe interference patterns with single photons, demonstrating wave-particle duality and determining the photon wavelength.
Malus’ Law for Single Photons: Students can investigate the polarization properties of single photons and confirm that their probability of passing through a linear polarizer follows Malus' Law, similar to classical electromagnetic waves.
Quantum Eraser Experiment: This advanced experiment demonstrates how "which-way" information, which destroys interference, can be "erased" by a suitable polarizer, thereby recovering the interference pattern.
Additional Experiments: The kit supports further investigations such as determining the coherence length of the SPDC source and exploring the "Three-Polarizer-Paradox" to understand quantum measurement. It also provides an optical implementation of the Deutsch-Jozsa algorithm for introductory quantum computing concepts.

Important Technical Specifications:

Laser Diode: Class 3B laser diode, L405P20, emitting more than 50 mW of optical power at 405 nm (±5 nm). It has an elliptical beam shape (3 mm x 1 mm) and a divergence in the mrad range.
Single Photon Detectors (SPDMA): Operate in Geiger mode, with a spectral detection efficiency of approximately 45% at 810 nm and a maximum efficiency of 65% at 600 nm. They have a dead time of <35 ns and a maximum count rate of 20 MHz. Typical dark count rates are <300 Hz.
Time Tagger (EDU Time Tagger): Features four active channels with a jitter of <720 ps. It assigns precise timestamps to detector events, allowing for post-processing to calculate coincidences and time differences.
BBO Crystal: Type-I BBO crystal, 3 mm thick, with a cutting angle of 29.2° for optimal phase matching of 405 nm pump photons to 810 nm signal/idler photon pairs.
Michelson Interferometer Stage (NFL5DP20S(/M)): 5 mm travel translation stage with a differential drive and 20 µm closed-loop piezo driver, controlled by a KPZ101 K-Cube Piezo Controller and KSG101 K-Cube Strain Gauge Controller for precise mirror movement.
Polarizers: Includes LPNIRE100-B (Ø1") and LPNIRB050 (Ø1/2") linear polarizers. The LPNIRB050 polarizers have a parallelism of <0.5 arcmin, making them suitable for interferometer use.
Axicon: Ø1/2" axicon with a 3° half opening angle for the light cone, designed to emulate the photon pair emission from the BBO crystal.
Bandpass Filters: Ø1" bandpass filters with a center wavelength (CWL) of 810 ± 2 nm and a FWHM of 10 ± 1 nm for detector optics.

Usage Features:

Open Design: Allows students to directly observe and manipulate each component, fostering a deeper understanding of the experimental setup.
Free Space Optics: Avoids optical fibers, which simplifies alignment and allows for direct placement of detectors within the system.
Time-Tagging Software: User-friendly software for data acquisition, real-time display of count rates and correlation functions, delay adjustment, and saving results. It includes dedicated tabs for HBT, GRA, Malus' Law, and Michelson Interferometer experiments.
Alignment Aids: Includes various tools and procedures for precise alignment, such as alignment targets, irises, and detailed step-by-step instructions for collimating lasers, positioning optics, and fine-tuning detectors.
Safety Features: The laser driver is equipped with a key switch and safety interlock. Laser safety glasses (LG3) are included and recommended for use with the Class 3B laser. Piezo controller warnings highlight high voltage outputs and precautions.
Configurable Settings: Software settings can be customized and saved, including laser current, automatic laser control, and detection schemes. Default settings can be restored.

Maintenance Features:

Software Installation: The kit includes a USB stick with all necessary software installers (EDU-QOP1, Thorlabs Kinesis, Swabian Instruments Time Tagger, dotnet-runtime). Updates are available online.
Troubleshooting Guide: A comprehensive section addresses common issues such as pump laser malfunction, low count rates, and problems with specific experiments, offering solutions and tips for optimization.
Environmental Considerations: Recommendations for operating in a darkened room to minimize background light and suggestions for wavelength filtering enclosures to mitigate sunlight interference.
Thermal Stability: For Michelson interferometer experiments, it is noted that replacing the aluminum breadboard with stainless steel and housing the interferometer in a box can reduce thermal drift and air current fluctuations, improving signal stability.
Calibration Procedures: Detailed instructions for calibrating polarizers and the Michelson interferometer stage ensure accurate measurements.
Component Replacement: Information on how to contact Thorlabs Tech Support for replacement parts and assistance.
Return of Devices: Guidelines for returning devices for servicing, emphasizing the importance of original packaging.