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Laser Physics Letters

Experimental realization of counterfactual quantum cryptography

G. Brida, Andrea Cavanna, Ivo Pietro Degiovanni, Marco Genovese, P. Traina

Published Jan 16, 2012• 56 citations
Publisher

Abstract

In counterfactual quantum key distribution (CQKD) information is transferred, in a secure way, between Alice and Bob even when no particle carrying the information is in fact transmitted between them. In this letter we fully implement the scheme for CQKD proposed in [1], demonstrating for the first time that information can be transmitted between two parties without the transmission of a carrier.

DOI
10.1002/lapl.201110120

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In counterfactual quantum key distribution (QKD), two remote parties can share a secure \nsecret random key even without transmission of a physical particle (a non-vacuum pulse) through the \nchannel. A QKD scheme is proposed which is counterfactual in one of the bits, and in which the secret bits \nare not encoded in the polarization, but in the joint action of Alice and Bob. On the conceptual level, our \nscheme throws new light on the origin of security in counterfactual cryptography. On the practical side, \nnon-polarization encoding makes it robust against certain trojan horse attacks. We study the the general \nphoton-number preserving incoherent attack in detail.

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In counterfactual quantum key distribution (CQKD) information is transferred, in a secure way, between Alice and Bob even when no particle carrying the information is in fact transmitted between them. In this letter we fully implement the scheme for CQKD proposed in [1], demonstrating for the first time that information can be transmitted between two parties without the transmission of a carrier.
Quantum cryptography allows one to distribute a secret key between two remote parties using the fundamental principles of quantum mechanics. The well-known established paradigm for the quantum key distribution relies on the actual transmission of signal particle through a quantum channel. In this Letter, we show that the task of a secret key distribution can be accomplished even though a particle carrying secret information is not in fact transmitted through the quantum channel. The proposed protocols can be implemented with current technologies and provide practical security advantages by eliminating the possibility that an eavesdropper can directly access the entire quantum system of each signal particle.
Quantum effects, besides offering substantial superiority in many tasks over classical methods, are also expected to provide interesting ways to establish secret keys between remote parties. A striking scheme called "counterfactual quantum cryptography" proposed by Noh [Phys. Rev. Lett. 103, 230501 (2009).] allows one to maintain secure key distributions, in which particles carrying secret information are seemingly not being transmitted through quantum channels. We have experimentally demonstrated, for the first time, a faithful implementation for such a scheme with an on-table realization operating at telecom wavelengths. To verify its feasibility for extension over a long distance, we have furthermore reported an illustration on a 1 km fiber. In both cases, high visibilities of more than 98% are achieved through active stabilization of interferometers. Our demonstration is crucial as a direct verification of such a remarkable application, and this procedure can become a key communication module for revealing fundamental physics through counterfactuals.
In counterfactual quantum key distribution (QKD), two remote parties can securely share random polarization-encoded bits through the blocking rather than the transmission of particles. We propose a semi-counterfactual QKD, i.e. , one where the secret bit is shared, and also encoded, based on the blocking or non-blocking of a particle. The scheme is thus semi-counterfactual and not based on polarization encoding. As with other counterfactual schemes and the Goldenberg-Vaidman protocol, but unlike BB84, the encoding states are orthogonal and security arises ultimately from single-particle non-locality. Unlike any of them, however, the secret bit generated is maximally indeterminate until the joint action of Alice and Bob. We prove the general security of the protocol, and study the most general photon-number–preserving incoherent attack in detail.
In counterfactual quantum key distribution (QKD), two remote parties can share a secure \nsecret random key even without transmission of a physical particle (a non-vacuum pulse) through the \nchannel. A QKD scheme is proposed which is counterfactual in one of the bits, and in which the secret bits \nare not encoded in the polarization, but in the joint action of Alice and Bob. On the conceptual level, our \nscheme throws new light on the origin of security in counterfactual cryptography. On the practical side, \nnon-polarization encoding makes it robust against certain trojan horse attacks. We study the the general \nphoton-number preserving incoherent attack in detail.