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Quantum Communications and Networks

Summary

The Quantum Communication and Networks Project develops quantum devices and studies them for use in quantum communications and networking applications. Our goal is to bridge the gap between fundamental quantum mechanics/information theory and their practical applications in information technology.

Our research covers two areas:
1. We perform research on the creation, transmission, transduction/interfacing, storage, processing and measurement of optical qubits – the quantum states of single photons. We build and study quantum devices, such as entangled-photon sources, single-photon detectors, optical quantum memory and quantum transduction/interfaces. A long-term goal is to apply these devices into quantum systems such as a quantum repeater. 
2. We are working toward implementing a quantum network testbed in which the suitability and performance of new and existing quantum devices and systems can be studied in a real-life network environment. The testbed will lead to the development of best-practices and protocols for quantum networks. 

Description

 A long term goal of our research is to implement a quantum repeater or quantum node, which can extend the transmission distance of quantum communications or connect the different quantum computing technologies of the future quantum internet.

Two distant points connected by quantum repeater. Key elements of repeater, including single photon sources and detectors, quantum interfaces and quantum memory, are shown below.
A quantum repeater can extend the distance of quantum communications. Essential components include single photon sources and detectors, quantum interfaces and quantum memory. 

Single Photon Sources:
An ideal single photon entangled pair source for a quantum repeater application should satisfy several conditions simultaneously. Since photons must interact efficiently with a quantum memory, the source must emit photons that are spectrally very pure (have a very narrow linewidth) and are aligned to the narrow energy transitions of the atomic ensemble used in the quantum memory.

A quantum repeater for long distance transmission requires pairs of ‘non-degenerate’ photons in which one photon at an atomic wavelength is suitable for quantum memory and the other photon at a telecom wavelength is suitable for long distance transmission in optical fibers. Alternatively, the photons may be degenerate (same wavelength) but compatible with a conversion quantum Interface that can alter their wavelength while preserving their quantum statistical properties.

Quantum Memory:
In a quantum repeater scheme, photons arriving at a Bell state measurement device must interfere. This is a very technically challenging process for single photons since they must arrive at the exact same point on a beam-combiner at the exact same time. To achieve this, quantum memories can be used to store the quantum property of each photon until they are all available and ready, and then release the photons in a controlled way onto the beam-combiner for more efficient interference.

Our current research includes the implementation a quantum memory scheme called Electromagnetically Induced Transparency (EIT) in an ensemble of Cesium atoms, in which a laser control beam can turn ‘on’ or ‘off’ the storage of a single photon level signal.

Quantum Interface:
A quantum interface is needed when different photon characteristics are optimal for certain tasks such as long-distance transmission, efficient detection or different quantum computing technology. For example, photons at wavelengths that are suitable for long distance transmission in optical fibers are not optimal for easy and efficient detection. A quantum interface in this case can convert the photons from the telecommunications band for transmission to the near visible band for detection while preserving the quantum statistical properties of the photons. On the other hand, photon pairs generated at atomic resonance wavelengths may need to be converted to a telecommunications band for long distance transmission. As another example, different quantum computing technologies rely on different wavelength photons. Transferring qubit states from photons at one wavelength to the other is necessary for connecting  or scaling quantum computers.

Quantum Network Testbed: 
The Platform for Quantum Network Innovation (PQNI) will be a quantum extension of NISTs Platform for Network Innovation (PNI) and will be used to test and develop quantum networking layers and control planes; develop best practices and protocols for classical/quantum co-existence; study of quantum edge-nodes/interfaces (physical and logical); study quantum device performance; study vulnerabilities (such as eavesdroppers) and robustness; and incorporate complex quantum systems such as quantum repeaters.

About us:
We perform research and development on quantum repeaters and supporting measurement technologies. Our mission is to bridge the gap between fundamental quantum research and practical information technology applications. Our research aims to promote US innovation, industrial competitiveness and enhance the nation's security. For more information, contact project leader Dr. Oliver Slattery. For more information concerning the ITL Quantum Information program, please select link 'ITL Quantum Information Program'.

Positions available:
We have interesting experimental optics positions available for Postdocs and/or Guest Researchers in the Quantum Communications Project. Candidates should have an interest in experimental optics and be motivated to perform research independently. For more information, please contact oliver.slattery [at] nist.gov (subject: Inquiry%20from%20Quantum%20Communication%20Project%20website) (Dr. Oliver Slattery.) 

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A general quantum repeater shows photons from a pair of entangled photon sources moving towards a BSM via quantum memory.  After interfering in a BSM, these photons become entangled and the correlated photons at Alice and Bob also become entangled.
The goal of a quantum repeater is to generate entanglement between distant qubits at Alice and Bob. Initially, two entangled photon sources generate two pairs of photons - one from each pair being sent to the distant locations and the other photons in each pair being sent to a Bell State Measurement (BSM). In order to achieve a successful BSM, the photons are stored momentarily in quantum memory and released in a controlled way. The result of the BSM is classically communicated to Alice and Bob who will then know how to prepare their photons for the desired entanglement state.

Created November 22, 2016, Updated September 26, 2019