Characterization and manipulation of energy entangled qudits
André Stefanov, Christof Bernhard, Bänz Bessire, Thomas Feurer · 2013
Summary form only given. Entanglement is a fundamental resource for the quantum processing of information and to study the intrinsic nature of quantum correlations. Entangling higher dimensional bipartite systems (qudits) has been shown to give more insight on the nature of entanglement compared to the simplest entanglement system composed of two two level systems (two qubits) [1, 2]. For quantum key distribution, increasing the dimension of the alphabet by using qudits increases the effective bit rate of the protocol, still being secure [3]. Experimentally, higher dimensional entanglement in photonic systems have been demonstrated for various degrees of freedom of light, including time-bins [4,5], transverse momentum [6, 7] or orbital angular momentum modes [8].We demonstrate here a new way to encode qudits in the energy spectrum of the entangled photons by defining frequency bins within their spectra. Broadband entangled photons are generated by continuous wave spontaneous down-conversion and detected in coincidence by sum frequency generation. By means of experimental methods used for shaping fs-laser pulses, frequency bins can be addressed in the photons spectra. Furthermore, controlling each frequency component individually allows to manipulate and characterize the quantum states. The dimension of the generated states is in practice limited by the optical resolution of the setup only.