Quantum cryptography using femtosecond-pulsed parametric down-conversion

Sergienko, Alexander V.; Atatüre, Mete; Walton, Zachary D.; Jaeger, Gregg; Saleh, Bahaa E. A.; Teich, Malvin C.

doi:10.1103/physreva.60.r2622

Cited by 74 publications

(58 citation statements)

References 18 publications

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“…Scientists are currently using one of two photon sources for practical QKD, faint lasers [5,6,7,8,9,10] or spontaneous parametric down-conversion to generate entangled photon states (SPDC) [11,12,13,14,15].…”

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Modified Wigner inequality for secure quantum-key distribution

2003

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In this report we discuss the insecurity with present implementations of the Ekert protocol for quantum-key distribution based on the Wigner Inequality. We propose a modified version of this inequality which guarantees safe quantum-key distribution. QKD offers the possibility that two remote parties, conventionally called Alice and Bob, exchange a secret random key to implement a secure encryption-decryption algorithm, without meeting [1,2,3]. QKD provides a significant advantage over the public-key cryptography because the security of the distributed key relies on the laws of quantum physics [1, 2, 3], i.e. the wave packet collapse prohibits gaining information from a quantum channel without disturbing it. Indeed, any attempt by a third party (Eve) to obtain information about the key is detected.Two main goals underly the implementation of QKD schemes. One is to create and preserve authentic quantum channels against decoherence effects induced by any interaction with the environment [4], eventually reducing or even destroying invulnerability of quantum channels against Eve's attack. The other is to provide a true guarantee of absolute security against any possible eavesdropping attack i.e. the security is not simply based on technological feasibility.

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confidence: 99%

Modified Wigner inequality for secure quantum-key distribution

2003

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“…Unfortunately, femtosecond pulse pumped SPDC shows relatively poor quantum interference visibilities (Keller and Rubin, 1997). The following methods are used to increase the quantum interference visibility: (i) a thin nonlinear crystal (Sergienko et al, 1999), (ii) narrow-band spectral filters in front of detectors, as shown above (Grice and Walmsley, 1997;Grice et al, 1998;Di Giuseppe et al, 1997), or (iii) an interferometric technique (Branning et al, 1999(Branning et al, , 2000 without spectral and amplitude post-selection, which was making the spectral wave function of the two photons much more symmetric. 25 The first two methods reduce the intensity of the entangled photon pairs significantly and cannot achieve perfect overlap of the two-photon amplitudes.…”

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confidence: 99%

Multiphoton entanglement and interferometry

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Fortschritte der Physik

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Multi-photon interference reveals strictly non-classical phenomena. Its applications range from fundamental tests of quantum mechanics to photonic quantum information processing, where a significant fraction of key experiments achieved so far comes from multi-photon state manipulation. We review the progress, both theoretical and experimental, of this rapidly advancing research. The emphasis is given to the creation of photonic entanglement of various forms, tests of the completeness of quantum mechanics (in particular, violations of local realism), quantum information protocols for quantum communication (e.g., quantum teleportation, entanglement purification and quantum repeater), and quantum computation with linear optics. We shall limit the scope of our review to "few photon" phenomena involving measurements of discrete observables.

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“…This confirms Eq. (8). In other words, we have successfully prepared polarization Bell states from femtosecond pulsepumped SPDC without amplitude and spectral postselection.…”

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“…One has to utilize special experimental schemes to achieve complete overlap of the twophoton amplitudes. Traditionally, the following methods were used to restore the quantum interference visibility in femtosecond pulse pumped type-II SPDC: (i) use a thin nonlinear crystal (≈ 100µm) [8] or (ii) use narrow-band spectral filters in front of detectors [6,7]. Both methods, however, reduce the available flux of the entangled photon pair significantly [9] and cannot achieve complete overlap of the wave-functions in principle [6].…”

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confidence: 99%

Bell-state preparation using pulsed nondegenerate two-photon entanglement

2001

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We report a novel Bell state preparation experiment. High-purity Bell states are prepared by using femtosecond pulse pumped nondegenerate collinear spontaneous parametric down-conversion. The use of femtosecond pump pulse does not result in reduction of quantum interference visibility in our scheme in which post-selection of amplitudes and other traditional mechanisms, such as, using thin nonlinear crystals or narrow-band spectral filters are not used. Another distinct feature of this scheme is that the pump, the signal, and the idler wavelengths are all distinguishable, which is very useful for quantum communications.PACS Number: 03.67. Hk, 03.65.Bz, 42.50.Dv Preparation and measurement of the Bell states are two important issues in modern quantum optics, especially for quantum communications, quantum teleportation, etc [1]. For photons, such states can be realized by using the entangled photon pairs generated in spontaneous parametric down-conversion (SPDC). By making appropriate local operations on the SPDC photon pairs, one can prepare all four Bell states.The polarization Bell states, for photons, can be written aswhere the subscripts 1 and 2 refer to two different photons, photon 1 and photon 2, respectively, and they can be arbitrarily far apart from each other. |X and |Y form the orthogonal basis for the polarization states of a photon, for example, it can be horizontal ( |H ) and vertical (|V ) polarization state, as well as |45 • and |−45 • , respectively. This means that the quantum interference should be independent of the choice of the bases. Such an experiment was first performed by Shih and Alley in which non-collinear type-I SPDC and a beamsplitter were used to prepare a Bell state [2], but it is very difficult to align such a system. Collinear type-II SPDC is thus developed [3]. There is, however, a common problem: the entangled photon pairs have 50% chances of leaving at the same output ports of the beamsplitter. Therefore, the state prepared after the beamsplitter may not be considered as a Bell state without amplitude postselection [4]. Only when one considers the coincidence contributing terms by throwing away two out of four amplitudes (post-selection of 50% of the amplitudes), the state is then said to be a Bell state. This problem is later solved by using non-collinear type-II SPDC or using two non-collinear type-I SPDC [5]. * Email: yokim@umbc.edu † Permanent address: Department of Physics, Moscow State University, Moscow, 119899, Russia.In the cw pumped SPDC, entangled photon pairs occur randomly since the process is "spontaneous", so whereabouts of the photon pair is completely uncertain within the coherence length of the pump laser beam. This huge time uncertainty makes it difficult for applications such as generation of multi-photon entangled state, quantum teleportation, etc, as interactions between entangled photon pairs generated from different sources are required. This difficulty was thought to be solved by using a femtosecond pulse laser as a pump. Unfortunately, femtosecond...

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Quantum cryptography using femtosecond-pulsed parametric down-conversion

Cited by 74 publications

References 18 publications

Modified Wigner inequality for secure quantum-key distribution

Modified Wigner inequality for secure quantum-key distribution

Multiphoton entanglement and interferometry

Bell-state preparation using pulsed nondegenerate two-photon entanglement

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