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Quantum Cryptography Analogy Demonstration Kit
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Binary information encoded in the polarization state of light is detected by a sensor module (indicated by a blue LED).
Quantum Cryptography Analogy Demonstration Kit
The EDU-QCRY1(/M) Quantum Cryptography Analogy Demonstration Kit contains components to model a data transmission setup using the BB84 encryption protocol. This encryption method allows a sender and receiver to generate an encryption key that only they know and eavesdroppers to be detected. In this analogy experiment, the polarization of transmitted light carries bits of information which are manipulated using half-wave plates and polarizing beamsplitters. The educational lab kit includes the lasers, half-wave plates, polarizing beamsplitters, and detectors required to model the sender (Alice), the receiver (Bob) and the eavesdropper (Eve).
Please note that this is a classical experiment that simulates the key principles used in quantum cryptography. As an analogy to the quantum setup, this experiment works with a pulsed laser instead of single photons. Single photon detectors are not included in this kit.
Thorlabs Educational Products
Thorlabs' line of educational products aims to promote physics, optics, and photonics by covering many classic experiments, as well as emerging fields of research. Each educational kit includes all the necessary components and a manual that contains both detailed setup instructions and extensive teaching materials. These lab kits are being offered at the price of the included components, with the educational materials offered for free. Technical support from our educational team is available both before and after purchase.
Purchasing Note: English and German language manuals/teaching information are available for this product. The imperial educational kit contains the English manual and US-style power cords. The appropriate manual and power cords will be included in the metric kit based on your shipping location. The power supplies and other electronic devices in both the metric and the imperial kit accept voltages of 230 VAC and 120 VAC. Please contact Tech Support if you need a different language, cord style, or power supply. As with all products on our website, taxes are not included in the price shown below.
This kit is designed to demonstrate the fundamentals of quantum cryptography and the BB84 encryption protocol through a series of classroom experiments. In these experiments, students will learn how to encode messages in binary using the polarization state of light and then encrypt them using the BB84 protocol.
The BB84 Protocol
However, the fundamental challenge is ensuring that only Alice and Bob have knowledge of the encryption key and preventing an eavesdropper (designated as Eve) from intercepting the encryption key. The BB84 encryption protocol uses the idea of quantum key distribution (QKD) to ensure that only Alice and Bob have knowledge of the encryption key. QKD employs principles of quantum physics, such as the encoding of a single bit of information within a photon of light, to ensure that the information cannot be copied. Any interception attempt by Eve will inevitably change the state of the photon. Thus, the BB84 protocol offers the ability to send truly secure encrypted transmissions.
Modeling the BB84 Protocol Using the Polarization of Light
In this experiment, the eavesdropper (Eve) is represented by a module that can receive a transmission from Alice and then attempt to send the same signal to Bob. While Eve is free to do this since the "transmission" is public, students will learn how this will cause errors that reveal the presence of an eavesdropper. Because detection of an eavesdropper occurs during transmission of the encryption key, once Alice and Bob have verified that there is no eavesdropper, the message can be sent without risk of interception.
Single Photons Versus Classical Light
Please note that the EDU-QCRY1(/M) analogy kit uses a pulsed laser source, i.e. classical light. While the sequence of the protocol is completely identical to the true quantum encryption system, it cannot be used as a perfect encryption system. Eve is able to eavesdrop unnoticed by separating a portion of the transmitted light for analysis while the remainder is sent to Bob.
This tab illustrates an example exercise that can be done by students using the EDU-QCRY1(/M) Quantum Cryptography Analogy Demonstration Kit. For full details on exercises and worksheets for students, please refer to the manual.
This example illustrates the generation of an encryption key between Alice and Bob, and the transmission a 10-bit, two-letter encrypted message using the BB84 protocol.
Generating an Encryption Key
At the same time, Bob chooses a random set of bases to use in receiving the transmission. These bases are chosen independently from Alice and will not always match. After transmission, Alice and Bob compare bases that they used. In cases where the basis matches with the one chosen by Alice (highlighted in green in Table 2), Bob will obtain the same bit as chosen by Alice. However, if the basis does not match, Bob will randomly receive a 0 or 1. Because the result is random, these bits are thrown out; the remaining green-highlighted bits become the encryption key between Alice and Bob.
In this example, the encryption key would be the sequence: "0 1 1 0 0 1 0 0 0 1".
Sending an Encrypted Message Using an Encryption Key
To encrypt the message, Alice performs binary addition on the message and encryption key (see the table below for addition rules). The resulting 10-bit message can then sent from Alice to Bob through public channels and using a previously agreed upon basis (i.e., Alice and Bob both choose to use either a + or × basis). After transmission, Bob can then decode the message by using binary addition on the encrypted message key using the encryption key. Because the results of binary addition are reversible, adding in this fashion returns the original binary message.
This method for sending secure messages, however, assumes that no eavesdropper has knowledge of the encryption key. Because the transmissions described above are carried out via public channels, Eve can try to intercept the encryption key by intercepting the transmission between Alice and Bob. However, doing so will cause errors in the transmission. In the BB84 protocol, after comparing bases (Table 2), Alice and Bob will compare a test region of the encryption key. The errors introduced by Eve can be found by Alice and Bob when comparing the test region, alerting them to the presence of the eavesdropper. For a more detailed example, see Section 6.2 of the manual.
Quantum Cryptography Analogy Demonstration Kit Components
Thorlabs' Quantum Cryptography Analogy Demonstration Kit is available in imperial and metric versions. In cases where the metric and imperial kits contain parts with different item numbers, metric part numbers are listed next to their imperial counterpart and measurements are indicated in parenthesis.
Imperial Kit: Included Hardware and Screws
Metric Kit: Included Hardware and Screws
The EDU-QCRY1(/M) was developed in cooperation with several educators and organizations specializing in teaching quantum physics:
Do you have ideas for an experiment that you would like to see implemented in an educational kit? Contact us at email@example.com; we'd love to hear your ideas.