Increasing the orbital angular momentum bandwidth of entangled photons

Jacquiline Romero; Daniele Giovannini; Sonja Franke-Arnold; Stephen M. Barnett; Miles J. Padgett

doi:10.1117/12.979888

19 November 2012 Increasing the orbital angular momentum bandwidth of entangled photons

Jacquiline Romero, Daniele Giovannini, Sonja Franke-Arnold, Stephen M. Barnett, Miles J. Padgett

Proceedings Volume 8542, Electro-Optical Remote Sensing, Photonic Technologies, and Applications VI; 85421S (2012) https://doi.org/10.1117/12.979888
Event: SPIE Security + Defence, 2012, Edinburgh, United Kingdom

Abstract

The bandwidth of any communication system, classical or quantum, is limited by the number of orthogonal states in which the information can be encoded. Quantum key distribution systems available commercially rely on the two-dimensional polarisation state of photons. Quantum computation has also been largely designed on the basis of qubits. However, a photon is endowed with other degrees of freedom, such as orbital angular momentum (OAM). OAM is an attractive basis to be used for quantum information because it is discrete and theoretically infinite-dimensional. This promises a higher information capacity per photon which can lead to more complex quantum computation protocols and more security and robustness for quantum cryptography. Entanglement of OAM naturally arises from spontaneous parametric down-conversion (SPDC). However, any practical experiment utilising the innately high-dimensional entanglement of the orbital angular momentum (OAM) state space of photons is subject to the modal capacity of the detection system. Only a finite subset of this space is accessible experimentally. Given such a constraint, we show that the number of measured, entangled OAM modes in photon pairs generated by SPDC can be increased by tuning the phase-matching conditions in the SPDC process. We achieve this by tuning the orientation angle of the nonlinear crystal generating the entangled photons.

Citation Download Citation

Jacquiline Romero, Daniele Giovannini, Sonja Franke-Arnold, Stephen M. Barnett, and Miles J. Padgett "Increasing the orbital angular momentum bandwidth of entangled photons", Proc. SPIE 8542, Electro-Optical Remote Sensing, Photonic Technologies, and Applications VI, 85421S (19 November 2012); https://doi.org/10.1117/12.979888

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KEYWORDS

Photons

Crystals

Spatial light modulators

Quantum information

Lithium

Laser crystals

Signal detection

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