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A Science Kit for Quantum Physics.

  • quED Entanglement Demonstrator - A Science Kit for Quantum Physics
  • Overview
  • Sample Experiments
  • Add-Ons
  • Key Features
  • Photon Source
  • References
  • Applications
  • System Includes
  • Videos
  • Downloads & Links

Quantum mechanics is deeply rooted in the heart of modern physics. But it is not easy to teach. Quantum theory often contradicts our everyday life experience and the corresponding experiments are neither easy to setup nor to maintain.When Aspect, Roger and Dalibard showed that entangled photons violate Bell’s inequality for the first time in 1982, their setup filled the whole basement lab. The quED fits on any lab desk and can be set up in minutes. And it is more accurate and a lot more efficient than the apparatus of Aspect and his colleagues.

qutools’ Entanglement Demonstrator is designed for educational purposes. The easy-to-use system frees the hands and brains of anyone trying to explain the complex phenomena of quantum mechanics. Because that’s already hard enough.

quED: “Spooky action at a distance”? Not so spooky anymore…

It’s a science project kit for modern physics.

Sample Experiments

Here is a list of the experiments you can do with the quED and its add-ons.

Single Photon Experiments without Interference
Particle Nature of Photons
Quantum Cryptography/QKD: BB84 Protocol
Quantum Random Number Generation
Single Photon Experiments with Interference
Wave Nature of Photons: Single Photon Michelson Interferometer
Quantum Eraser
Wave-Particle Dualism: Michelson + HBT
Photon Pair Experiments with Polarisation Entanglement
Violation of Bell’s Inequality (CHSH)
“Non-Classical” Polarisation Correlations
Photon Pair Experiments without Polarisation Entanglement
Hong-Ou-Mandel 2-Photon Interference
Hong-Ou-Mandel Interference + Hanbury Brown & Twiss
Franson Interference

These are the experiments we have come up with so far and found interesting enough to put them here. Do you have more ideas? Please let us know!

The functionality of the quED system can easily be extended with these add-ons:

+ quED-MI Michelson Interferometer

Demonstrate the wave nature of single photons through their interference or build a quantum eraser.

Single Photon Michelson Interferometer Add-On for the quED.

  • Single Photon Michelson Interferometer Add-On for the quED.

Interference is generally considered to be a wave phenomenon. Curiously it also works with single quantum objects. Use the quED-MI Michelson Interferometer add-on together with the quED to show that this is the case. (The photograph shows the motorised version.)

Read more about the quED-MI Michelson Interferometer.

+ quED-HBT Hanbury Brown Twiss
Perform the “Grangier Experiment”, explore the particle nature of single photons with a Hanbury Brown & Twiss setup and build a quantum random bit generator.

Hanbury Brown & Twiss Setup for Heralded Single Photon Sources.

  • Hanbury Brown-Twiss setup Add-On for the quED

Photons (or generally quantum objects) sometimes also behave like particles. With this add-on you can show that photons can not be split up. You can also explore a simple quantum random bit/number generator and use it in combination with the quED-MI to show wave and particle nature of photons in one experiment.

Read more about the quED-HBT.

+ quED-HOM Hong–Ou–Mandel Effect
Experience the purely quantum 2-photon interference effect by revealing the Hong-Ou-Mandel dip.

Hong-Ou-Mandel Interferometer Demonstrating 2-Photon Interference.

  • Hong-Ou-Mandel effect Add-On for the quED

When you have two indistinguishable photons and each of them hit one input of a beam splitter, they exit the beam splitter together in one output port. This is an effect you cannot demonstrate with bright light, but with this add-on you can.

Read more about the quED-HOM.

+ quED-QKD Quantum Cryptography

Securely distribute a secret key between Alice and Bob with the BB84 protocol.

Quantum Cryptography Add-On for the quED.

One of the most popular industrial applications for quantum phenomena right now is quantum cryptography, or better, quantum key distribution. With this add-on, you can use weak coherent pulses to simulate realistically how a secure communication between two parties (Alice and Bob) is made possible by the BB84 protocol in a real environment.

Read more about the quED-QKD.

+ quED-TOM Quantum State Tomography
The quED-TOM let you determine the full quantum state density matrix that defines all properties of either a single photonic qubit or even the two-qubit entangled or non-entangled state that can be produced in the quED source.

Quantum State Tomography Setup

  • Setup of the manual 2-photon tomography with the quED.

A quantum mechanical state can not be determined using only a single measurement. But, if you have an ensemble of equally prepared states, as, e.g., by our SPDC source, there is a procedure that makes the complete determination of the quantum state, i.e. its density matrix, possible.

Read more about the quED-TOM.

Key Features

The quED design combines recent achievements of quantum optics technology into an easy-to-use system for academic, research and applied purposes with precise accuracy. Advanced models for scientific purposes are available as well, with a high performance meeting the requirements of state-of-the-art physics experiments. See how the SPDC source works.

  • Hands-on study of quantum entanglement
  • Compact design, user-friendly operation
  • Complete system: Ready to violate Bell’s inequalities
  • High performance: Entanglement verification in only a few seconds
  • Optional: Add-ons to extend the number of experiments

Animated Entangled Photon Source

LaseriThe pump laser diode emits light with a wavelength of λ = 405 nm and vertical polarization.
HWPiThe half waveplate rotates the polarization of linearly polarized light. Here, the vertical pump light can be rotated to +45° polarized light.
YVOiThe group-velocity mismatch between the pump and the down-conversion light in the birefringent BBO crystals causes the photon pairs born in the first crystal to be advanced with regard to those originating from the second. This birefringent YVO4 pre-compensation crystal negates this effect.
YVOiThe photons originating from the first BBO crystal experience higher dispersive delay due to their pass through the second BBO crystal. Consequently, a compensation using another birefringent YVO4 crystal has to be applied.
BBOiThe optical axis of the second BBO crystal is oriented at a 90° angle in comparison to the optical axis of the first crystal. This makes the process of down-converting horizontal pump photons to vertical output photon pairs possible.
BBOiA BBO crystal is a highly non-linear medium, making spontaneous parametric down conversion possible. Conservation of energy and momentum hold when a pump photon (vertically polarized) is converted into two output photons (horizontally polarized) with half the energy at λ = 810 nm.

Optical FibersiThe fiber couplers spatially select the photons to be detected. For best entanglement quality, their position and orientation has to be fine tuned such that photons from both BBO crystals are coupled with the same probability.

Dirac Notation:|V⟩|V⟩+|H⟩|V⟩|V⟩|V⟩+|H⟩|H⟩|HH⟩|VV⟩|VV⟩+|HH⟩|VV⟩|HH⟩

SPDC generates entangled photon pairs

The heart of the quED and Quantenkoffer is made out of β-Barium-Borate (BBO), a special optical non-linear crystal. A high power UV diode laser at 405 nm wavelength, called the pump laser, is focused in this crystal. If the polarization of the pump beam and the axis of the BBO crystal are matched in a way enabling energy and momentum conservation, some of the pump photons are converted into two lower energy near infrared photons at 810 nm. These down con-verted photons then emerge at opposite sides of a so-called emission cone and form a photon pair.

Even though the conversion rate is low (only about 1 of pump photons is converted), these photon pairs are quite useful, since whenever you observe a photon on one side, you know that there must be one on the other side, too! Therefore, you call them heralded single photons, and they can then be used in further experiments.

It becomes even more interesting if you add another BBO crystal with the optical axis perpendicular to the first one, condition the pump laser polarization by inserting a half wave plate (HWP) and compensate some temporal shifts and dispersion effects by two Ytterbium Vanadate (YVO) crystals: The photon pairs from the two crystals are coherently overlapped, so one cannot distinguish between pairs originated from the first or second crystal.

This is the condition for creating polarization entanglement between the photons of one such pair.

See also the brochure of the quED for more information.

For further informations at


Sebastian Will, Columbia University, NYC: “We have used the QuED setup here at Columbia University for remote instruction in our physics majors lab. Students are extremely excited using the setup and it motivates them to study the foundations of quantum entanglement in great depth. I have rarely seen students putting that much effort into a lab class as with this setup! It really makes entanglement tangible. At the same time it equips them with know-how that is essential in these times of emerging quantum technologies.“

Dr. Edward F. Deveney, Bridgewater State University, MA: “There is a new generation of quantum books now, and I think that they get to the heart of quantum mechanics in a quicker more accessible way all based on the experiments. Exciting that qutools is leading the way on the experiment side that students and most universities can do. Together you are revolutionizing the way quantum is taught, experienced, and understood. In turn it will lead to next generation quantum technologies and engineering and hopefully a deeper insight to what quantum is really telling us. I am pleased and lucky to have access to both and push for others to see these new ways to teach – I have as much fun as my students do.“

George Musser, editor at Scientific American magazine and the author “Spooky Action at a Distance” and “The Complete Idiot’s Guide to String Theory” about the quED: “Do-it-yourself quantum spooky action! An experiment that used to fill a basement lab now fits on any table.”

Dr. Eleni Diamanti, Université Pierre et Marie Curie, Paris: “We use the quED in my laboratory as a central element for our teaching activities; it is always a great and guaranteed success thanks to its stability and reliability. We have also extensivley used it in experiments ranging from the demonstration of nonlocal quantum games (Phys. Rev. Lett. 2015) to the reference-frame-independent quantification of bipartire entanglement (Phys. Rev. A 2014), more experiments are underway. “

Dr. Ulrich Busk Hoff, Danmarks Tekniske Universitet: “At DTU Physics we are proud to have high-quality products from qutools which allow us to do engaging outreach and hands-on teaching of fundamental quantum physics. The quED is an impressive product that puts everyone in a position to experiment with quantum physics. Thanks to our setups from qutools, Bell’s inequality has finally been violated for the first time in Denmark.”

Further Reading

General Publications
Scientific Publications by our Customers
  • M. Neugebauer et al., Neural network quantum state tomography in a two-qubit experiment, arXiv preprint (2020): Preprint
  • A. Nomerotski et al., Counting of Hong-Ou-Mandel Bunched Optical Photons Using a Fast Pixel Camera, arXiv preprint (2020): Preprint
  • C. Ianzano et al., Spatial characterization of photonic polarization entanglement using a Tpx3Cam intensified fast-camera, arXiv preprint (2018): Preprint
  • G. Pütz et al., Quantum Nonlocality with Arbitrary Limited Detection Efficiency, Phys. Rev. Lett. 116, 010401 (2016): PRL | Preprint
  • D. Aktas et al., Demonstration of Quantum Nonlocality in the Presence of Measurement Dependence, Phys. Rev. Lett. 114, 220404 (2015): PRL | Preprint
  • A. Pappa et al., Nonlocality and Conflicting Interest Games, Phys. Rev. Lett. 114, 020401 (2015): PRL | Preprint
  • T. Lawson et al., Reliable experimental quantification of bipartite entanglement without reference frames, Phys. Rev. A 90, 042336 (2014): PRA | Preprint
  • E. Pomarico et al., Various quantum nonlocality tests with a commercial two-photon entanglement source, Phys. Rev. A 83, 052104 (2011): Institute Website | PRA


qutools’ Entanglement Demonstrator is designed with educators in mind. It’s the easiest and most reliable way to explain the complex phenomena of quantum mechanics by generating and analysing polarization-entangled photon pairs.

Specific applications are:

  • Student lab course experiments
  • Demonstration experiments in lectures
  • Hands-on experiments for science centers
  • Project kits for students’ research centers

For demonstration experiments, we propose to use the motorised version. When students are supposed to perform the experiments themselves, the manual versions are recommended.

System Includes

The standard quED package includes everything you need to violate Bell’s inequality and perform similar experiments.

  • Source of fiber-coupled polarization-entangled photon pairs
  • Two silicon single photon avalanche detectors
  • Alignment help utilities including auxiliary low-power visible laser module
  • Four-channel counter with integrated coincidence logic unit
  • Control and read-out unit

Have a look at our add-ons if you would like to perform additional experiments!



quED datasheet 10/2021 0.5 MB pdf
quED quickstart manual 10/2021 0.5 MB pdf
quED manual 10/2021 19.1 MB pdf
quCR manual 10/2019 5.0 MB pdf
quED brochure 10/2021 2.4 MB pdf


quED – Introduction 05/2020 video
quED – Violation of Bell’s Inequality 05/2020 video

Work Sheets & Courses

Alignment 04/2021 pdf
Bell’s Inequality 09/2019 pdf
Sample Lab Course 06/2022 pdf


Spontaneous parametric down-conversion 05/2020 animation
The Photon and the Second Order Correlation Function 04/2021 pdf