Practical implementation of multilevel quantum cryptography
- PDF / 271,547 Bytes
- 12 Pages / 612 x 792 pts (letter) Page_size
- 21 Downloads / 256 Views
LECULES, OPTICS
Practical Implementation of Multilevel Quantum Cryptography S. P. Kulika,*, G. A. Maslennikovb, and E. V. Morevac a Moscow
State University, Moscow, 119992 Russia University of Singapore, Singapore, 119077 Republic of Singapore c Moscow Engineering Physics Institute (State University), Moscow, 115409 Russia *e-mail: [email protected] b National
Received October 14, 2005
Abstract—The physical principles of a quantum key distribution protocol using four-level optical systems are discussed. Quantum information is encoded into polarization states created by frequency-nondegenerate spontaneous parametric down-conversion in collinear geometry. In the scheme under analysis, the required nonorthogonal states are generated in a single nonlinear crystal. All states in the selected basis are measured deterministically. The results of initial experiments on transformation of the basis polarization states of a four-level optical system are discussed. PACS numbers: 03.67.Hk, 42.25.Ja, 42.50.Dv DOI: 10.1134/S1063776106050037
1. INTRODUCTION The basic problems in classical cryptography are authentication and secure key distribution. The former means mutual verification of the identity of the legitimate partners. The latter means that the partners must have identical secret keys to be used for encryption and decryption. By Shannon’s coding theorem, an unconditionally secret key can be generated by a one-time pad as a random bit string at least as long as the transmitted message. However, generation of a new key for each message is an expensive procedure. The key distribution problem can be partially solved by using currently known algorithms, including so-called asymmetric cryptosystems. These are computationally secure in the sense that either the cost or complexity of breaking the key is too high (in the latter case, the message becomes worthless before the computations are completed). One example of asymmetric encryption is the Diffie–Hellman key exchange [1]. An alternative approach to the key distribution problem is quantum cryptography, in which quantum systems are employed as information carriers and quantum states can be used to generate unconditionally secret keys and easily change them. However, quantum key distribution does not solve the authentication problem. Quantum cryptography [2] appears to be the only achievement of quantum communication and quantum information science [3] that has been implemented on the hardware level. The unconditional security of a key distributed between the legitimate partners by using quantum systems is guaranteed by the no-cloning theorem, which states that an unknown quantum state can-
not be copied [4]. In the currently known quantum cryptosystems, information is encoded into nonorthogonal states of two-level systems (qubits). The most widely known protocols of this type make use of two (B92) [5], four [6], and six [7] states. However, a variety of alternative quantum cryptosystems have been discussed in the literature, including protocols using entangled states
Data Loading...
