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We present a proof of principle demonstration of a quantum key distribution scheme in higher-order -dimensional alphabets using spatial degrees of freedom of photons. Our implementation allows for the transmission of 4.56 bits per sifted photon, while providing improved security: an intercept-resend attack on all photons would induce an average error rate of 0.47. Using our system, it should be possible to send more than a byte of information per sifted photon.
Walborn et al. (Wed,) studied this question.