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T-EDU-QOP1 - Quantum Optics Educational Kit, Imperial

Fosco Connect Part No.: T-EDUQOP1

  • $ 38,250.00 or

T-EDU-QOP1 - Quantum Optics Educational Kit, Imperial

Product Manual

  • Includes Components to Investigate Quantum Properties of Light (Computer Not Included)
  • Requires a User-Supplied Optical Table or Breadboard with Damping Feet
  • Recommended Optical Breadboard and Damping Feet Sold Separately

T-EDU-QOP1(-M) Quantum Optics Educational Kit includes components to investigate quantum properties of light. This educational kit is offered in both an imperial and metric version.

This kit must be mounted on an optical table or breadboard, which is not included in this kit. If your lab does not already have a suitable one, we recommend the T-B2448FX (T-B60120AX) optical breadboard with the AV5(/M) damping feet, which are available for purchase separately below.

Quantum Description of Light

In quantum mechanics, light is described by quantized excitation of the electromagnetic field, where the smallest possible excitation is a single photon (with quantum number n = 1). Fock states are non-classical light states with a well-defined photon number (see the left graph of Figure 2).

Classical light, on the other hand, does not exhibit such a well-defined photon number. For example, light generated by a laser is in a coherent state. For a given mean photon number, the actual photon number follows a Poisson distribution (see the middle graph of Figure 2). Attenuation of the laser can only reduce the mean photon number while the underlying statistic remains Poissonian. Hence, an attenuated laser can never be used as a single photon source for quantum experiments.

Other classical light sources, such as LEDs or blackbody radiation, are described by thermal states, which are mixed quantum states, and exhibit an even larger variance of in photon number compared to laser light (see the right graph of Figure 2).

Generation of Single Photons

The term “single photons” refers to Fock states with photon number n = 1. A range of different sources can be used to generate single photons. Nowadays, most experiments use a process called Spontaneous Parametric Down-Conversion (SPDC) to generate photon pairs. The EDU-QOP1(/M) kit makes use of such a source, as it is rather simple to set up and offers stable operation, which makes it ideal for lab courses.

In SPDC, pump light generates two photons inside a nonlinear crystal, as seen in Figure 3. These photons are created virtually simultaneously, so that one of the photons can be used to signal the existence of the other, making it possible to perform measurements on single photons. For this reason, such a source is also called a heralded single photon source.

The T-EDU-QOP1 kit uses a β-Barium borate (BBO) crystal designed for a pump wavelength of 405 nm and a degenerate pair wavelength of 810 nm. The crystal is designed for a pair opening angle of 6° for spatially separated detection of both photons.

Coincidence Detection

Three SPDMA single photon detectors are used in the kit, as seen in the schematic in Figure 4. Similar to a Geiger-Müller counter, an incoming photon creates an electron avalanche in the detector, which is detected and converted into a TTL level output signal.

These three signal channels are analyzed by an educational-grade time tagger for coincidences between the detected events, as shown in Figure 5: for each event on the Trigger channel T it checks whether there is another event on channel A or B within a few nanoseconds wide window before or after. This time period is called the coincidence window. If the condition is met, a coincidence event is generated at the coincidence channels T&A or T&B. A triple coincidence occurs if all three detectors register a photon within the coincidence window.

For a pair source, the coincidences measured between both arms occur more often than for an uncorrelated light source. This can be characterized by the second order correlation function, g(2), which compares the expected coincidences for an uncorrelated light source with the measured coincidences:

where RA and RB are the average count rates of detectors A and B, respectively, RAB is the count rate of coincidences, and Δt is the time window.

In the Grangier-Roger-Aspect experiment (see the Experiments tab), the triple coincidences are compared to the rate expected for an uncorrelated (classical) light source by using the second order correlation function g(2)GRA:

where RTAB is the triple coincidence rate, RT is the count rate of the trigger detector T, and RTA and RTB are the coincidendence rates of detectors T and A and T and B, respectively. As a single photon pair is not able to trigger events on all three detectors, the triple coincidence rate is close to zero for a heralded single photon source and thus g(2)GRA << 1.

Easy Alignment

The kit uses two iris apertures to define a common beam path for the pump and alignment lasers. For each laser, two mirrors are used for beam walking, ensuring fast and repeatable alignment of the system using visible light.

An axicon is placed at the position of the BBO crystal to generate a cone of red light from the alignment laser, which mimics the cone of photon pairs from the BBO. Using this visible indicator, the detectors can be reliably aligned at the correct positions and orientations. The laser light cone can further be used for demonstration purposes.



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