NuCrypt, LLC Introduces Complete Quantum State Tomography System

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NuCrypt Expands Its Suite of Interoperable Quantum Optical Test and Measurement Equipment

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"Measurement equipment is critical to engineering... no such measurement equipment exists in the quantum space" Prof. Prem Kumar, NuCrypt Founder

NuCrypt, LLC—a company working to develop products that combine its expertise in photonics, electronics, and quantum effects—has expanded its line of quantum test and measurement equipment to include a Quantum State Tomography system, which is a unique combination of instruments and software that can reconstruct the quantum state of light. The counter-intuitive properties of quantum physics make quantum optical states useful for cutting-edge applications such as quantum communications and cryptography, but at the same time render quantum states inherently difficult to measure. Unlike in classical optics, quantum optical states cannot be determined via a single measurement. However, a series of incompatible measurements can be made and the full quantum state reconstructed from the measured values. The process, called Quantum State Tomography (QST), is similar to computer tomography (CT) in medical imaging where a 3-dimensional image is constructed from a series of 2-dimensional X-ray images.

The QST system can be used to reconstruct the quantum state of polarization entangled photon pairs, such as those emitted by NuCrypt’s entangled photon source EPS-1000. Two single-photon detectors behind automated polarization analyzers in the QST system measure correlations between the detected pairs of photons, thereby taking a polarization “image” of the two-photon quantum state. The polarization analyzers then change the measurement angles and the process is repeated. By making a series of measurements at various polarization angles, the underlying quantum state of polarization entanglement is reconstructed using a state reconstruction algorithm.

Although the technique of QST has been used in the research community for many years, no commercial equipment exists for such a purpose. Also, the complex measurement process tends to be very slow. For instance, using mechanical means to rotate wave plates for changing the polarization angles limits the transition time between successive measurements and thus increases the total time for QST. In order to speed up the QST system, NuCrypt developed a correlated photon detection system (CPDS-1000) with multiple high-speed (50MHz) single-photon counters and an automated polarization analyzer (PA-1000) which can accurately step through 36 different polarization measurement angles with less than 1ms transition time. The software to control the equipment and to store the resulting data is fully automated. The density matrix of the reconstructed quantum state and the associated metrics such as quantum state fidelity are computed and plotted on a computer screen. Quantum states can be measured and reconstructed in about one second, leading to near real-time monitoring of quantum entangled photon-pair sources of light. State fidelities of greater than 99% can be measured with the QST system.

“Measurement equipment is critical to engineering, and classical measurement equipment such as oscilloscopes and spectrum analyzers are routinely used,” notes Professor Prem Kumar, founder of NuCrypt LLC and director of the Center for Photonic Communication and Computing at Northwestern University. “No such measurement equipment exists in the quantum space, which is hindering research and applications development in the field of quantum information technology.” NuCrypt’s QST system and the associated technologies such as the fiber-coupled entangled photon-pair source aim to make the field more accessible to researchers and the quantum R&D process more efficient. The CPDS-1000 and PA-1000 are also sold separately for researchers working on component development.

About the company

NuCrypt is a privately held company founded in 2003. With core technology expertise in photonics, quantum effects, fiber optics, communications, and high speed electronics, it develops test equipment and applications in advanced photonics including quantum optics. For additional information, please see

For more information please contact:

Gregory Kanter
Vice President, NuCrypt, LLC
(847) 733-8750


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Greg Kanter
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