Complete experimental toolbox for alignment-free quantum communication

Vincenzo D’Ambrosio, Eleonora Nagali, Stephen Patrick Walborn +4 more

We developed a complete experimental toolbox to prove the communication possibility through the feasibility demonstration of a cryptographic-key distribution protocol, distribution of entanglement, and violation of a Bell inequality, all in alignment-free settings, i .e . by rotating the reference frame of the receiver.

Jonny Roberts, Matthew Young, Yasir J. Noori +4 more

Vincenzo D’Ambrosio, Eleonora Nagali, Stephen Patrick Walborn +4 more

Quantum communication employs the counter-intuitive features of quantum physics for tasks that are impossible in the classical world. It is crucial for testing the foundations of quantum theory and promises to revolutionize information and communication technologies. However, to execute even the simplest quantum transmission, one must establish, and maintain, a shared reference frame. This introduces a considerable overhead in resources, particularly if the parties are in motion or rotating relative to each other. Here we experimentally show how to circumvent this problem with the transmission of quantum information encoded in rotationally invariant states of single photons. By developing a complete toolbox for the efficient encoding and decoding of quantum information in such photonic qubits, we demonstrate the feasibility of alignment-free quantum key-distribution, and perform proof-of-principle demonstrations of alignment-free entanglement distribution and Bell-inequality violation. The scheme should find applications in fundamental tests of quantum mechanics and satellite-based quantum communication. Quantum communication promises important advances in information and communication technology, yet it suffers from alignment sensitivity. Here, an alignment-free approach is demonstrated using liquid crystal devices, allowing for broader applications, including satellites.

Mladen Pavičić

Omar Alshehri, Z.-H. Li, M. Al-Amri

Matthias M. Müller, Ressa S. Said, Fedor Jelezko +2 more

The chopped random basis (CRAB) ansatz for quantum optimal control has been proven to be a versatile tool to enable quantum technology applications such as quantum computing, quantum simulation, quantum sensing, and quantum communication. Its capability to encompass experimental constraints-while maintaining an access to the usually trap-free control landscape-and to switch from open-loop to closed-loop optimization (including with remote access-or RedCRAB) is contributing to the development of quantum technology on many different physical platforms. In this review article we present the development, the theoretical basis and the toolbox for this optimization algorithm, as well as an overview of the broad range of different theoretical and experimental applications that exploit this powerful technique.