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arXiv:quant-ph/0409111 · AIP conference proceedings

Energy-Time Entangled Qutrits: Bell Tests and Quantum Communication

Rob Thew

Published Jan 1, 2004• 0 citations
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Abstract

We have developed a scheme to generate, control, transmit and measure entangled photonic qutrits (two photons each of dimension d = 3). A Bell test of this source has previously been reported elsewhere, therefore, here we focus on how the control of the system is realized. Motivated by these results, we outline how the scheme can be used for two specific quantum protocols, namely key distribution and coin tossing and discuss some of their advantages and disadvantages.

DOI
10.1063/1.1834427

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Abstract. We have developed a scheme to generate, control, transmit and measure entangled photonic qutrits (two photons each of dimension d = 3). A Bell test of this source has previously been reported elsewhere [1], therefore, here we focus on how the control of the system is realized. Motivated by these results, we outline how the scheme can be used for two specific quantum protocols, namely key distribution and coin tossing and discuss some of their advantages and disadvantages. Performing quantum communication with high-dimensional systems would appear to be an obvious and straightforward extension to many of the qubit protocols that have driven quantum information science in recent years. There have been theoretical proposals for Quantum Key Distribution (QKD) [2] with greater security [3] as well as specific proposals for qutrits such as quantum coin tossing [4]. Fundamentally, high-dimensional Bell inequalities have revealed greater violations of non-locality [5] while increasing the dimensions of the entangled systems has been shown to facilitate closing the detection loop-hole [6] for such tests. Optics has been able to provide a realistic test-bed for these proposals with several different schemes being realized for generating high-dimensional entanglement [7, 8] as well as the scheme presented here [1, 9]. This source of entangled qutrits is analogous to the energy-time qubit arrangement of Franson [10]. The experimental scheme has been developed for telecom wavelengths and with proven long distance quantum communication architecture [11, 12] to optimise the usefulness of this high dimensional entanglement resource. We have already performed
We have experimentally realized a technique to generate, control and measure entangled qutrits, 3-dimensional quantum systems. This scheme uses spontaneous parametric down converted photons and unbalanced 3-arm fiber optic interferometers in a scheme analogous to the Franson interferometric arrangement for qubits. The results reveal a source capable of generating maximally entangled states with a net state fidelity, F = 0.985 ±\pm± 0.018. Further the control over the system reveals a high, net, 2-photon interference fringe visibility, V = 0.919 ±\pm± 0.026. This has all been done at telecom wavelengths thus facilitating the advancement towards long distance higher dimensional quantum communication.
We have performed a Bell-type test for energy-time entangled qutrits. A method of inferring the Bell violation in terms of an associated interference visibility is derived. Using this scheme we obtained a Bell value of $2.784\ifmmode\pm\else\textpm\fi{}0.023$, representing a violation of $34\ensuremath{\sigma}$ above the limit for local variables. The scheme has been developed for use at telecom wavelengths and using proven long distance quantum communication architecture to optimize the utility of this high dimensional entanglement resource.
We introduce a new technique to experimentally generate, control and measure entangled qutrits, 3-dimensional quantum systems. This scheme uses spontaneous parametric down converted photons and unbalanced 3-arm fiber optic interferometers in a scheme analogous to the Franson interferometric arrangement for qubits. The results reveal a source capable of generating maximally entangled states with a net state fidelity, F = 0.985 pm\\pmpm 0.018. Further the control over the system reveals a high, net, 2-photon interference fringe visibility, V = 0.919 pm\\pmpm 0.026, when the two phases are varied. This has all been done at telecom wavelengths thus facilitating the advancement to long distance higher dimensional quantum communication.
We produce two identical keys using, for the first time, entangled trinary quantum systems (qutrits) for quantum key distribution. The advantage of qutrits over the normally used binary quantum systems is an increased coding density and a higher security margin. The qutrits are encoded into the orbital angular momentum of photons, namely Laguerre–Gaussian modes with azimuthal index l + 1, 0 and −1, respectively. The orbital angular momentum is controlled with phase holograms. In an Ekert-type protocol the violation of a three-dimensional Bell inequality verifies the security of the generated keys. A key is obtained with a qutrit error rate of approximately 10%.