Pushing the limits of single-photon information content

Tristan Bernhard Horst Tentrup, Thomas Hummel, Allard P. Mosk +1 more

Thomas Hummel, Tristan Bernhard Horst Tentrup, Ravitej Uppu +2 more

Single photons are the carrier of choice in many quantum information processing protocols. Encoding information in a high-dimensional Hilbert space allows for the transfer of more than one bit of information per photon. We use a spatial light modulator (SLM) to direct the single photons to distinct positions of a virtual grid in the Fourier plane of the SLM. An electron-multiplying CCD (EMCCD) was used to detect the position of the photon at the receiver side. After analyzing the data, we conclude that, in contrast to an intensified CCD (ICCD), an EMCCD is not suited to detect the position of one single photon impinging on the camera in a single-shot measurement.

Teodor Strömberg

Tristan Bernhard Horst Tentrup, Willemijn M. Luiten, Peter Hooijschuur +2 more

Quantum Key Distribution (QKD) provides a secure way of generating shared cryptographic keys between a sender (Alice) and a receiver (Bob). The original BB84 protocol uses a two-dimensional polarization basis, limiting the information content of a single photon to 1 bit. Using the transverse position of single photons as one basis and the Fourier space as a second basis, one can construct a pair of mutually unbiased higher-dimensional bases. This improves not only the security of the protocol, but also the key generation rate. We present experimental results with a Spatial-Light-Modulator-based encoding scheme employing two nearly orthogonal alphabets with on the order of 103symbols each and an information content of about 10 bit.

Peter van Loock

This article reviews recent hybrid approaches to optical quantum information processing, in which both discrete and continuous degrees of freedom are exploited. There are well-known limitations to optical single-photon-based qubit and multi-photon-based qumode implementations of quantum communication and quantum computation, when the toolbox is restricted to the most practical set of linear operations and resources such as linear optics and Gaussian operations and states. The recent hybrid approaches aim at pushing the feasibility, the efficiencies, and the fidelities of the linear schemes to the limits, potentially adding weak or measurement-induced nonlinearities to the toolbox.

Tristan Bernhard Horst Tentrup, Thomas Hummel, Allard P. Mosk +1 more