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Characterization of an asynchronous source of heralded single photons generated at a wavelength of 1550 nm
KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
(English)Article in journal (Refereed) In press
Abstract [en]

We make a thorough analysis of heralded single photon sources regarding how factors such as the detector gate-period, the photon rates, the fiber coupling efficiencies, and the system losses affect the performance of the source. In the course of this we give a detailed description of how to determine fiber coupling efficiencies from experimentally measurable quantities. We show that asynchronous sources perform, under most conditions, better than synchronous sources with respect to multiphoton events, but only for nearly perfect coupling efficiencies. We apply the theory to an asynchronous source of heralded single photons based on spontaneous parametric downconversion in a periodically poled, bulk, KTiOPO4 crystal. The source generates light with highly non-degenerate wavelengths of 810 nm and 1550 nm, where the 810 nm photons are used to announce the presence of the 1550 nm photons inside a single-mode optical fiber. For our setup we find the probability of having a 1550 nm photon present in the single-mode fiber, as announced by the 810 nm photon, to be 48%. The probability of multiphoton events is strongly suppressed compared to a Poissonian light source, giving highly sub-Poisson photon statistics.

National Category
Telecommunications
Identifiers
URN: urn:nbn:se:kth:diva-9063OAI: oai:DiVA.org:kth-9063DiVA: diva2:14617
Note
QC 20100908Available from: 2006-02-10 Created: 2006-02-10 Last updated: 2010-09-08Bibliographically approved
In thesis
1. Entanglement in quantum communication: preparation and characterization of photonic qubits
Open this publication in new window or tab >>Entanglement in quantum communication: preparation and characterization of photonic qubits
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

At the heart of quantum physics lies the principle of superposition, and at the heart of information theory lies the bit. Perhaps the most useful property of quantum systems is that they can be loaded with information bits, so-called qubits, that are indefinitely both 0 and 1 until a measurement is made. Another consequence is that several qubits can become entangled, which is manifested by the non-classical correlations between such quantum systems when measured in all possible bases. Within the rapidly progressing fields of quantum information and quantum communication these quantum effects are utilized to perform tasks such as quantum computing and quantum cryptography.

In this thesis we present experimental and theoretical work using single photon sources to prepare ``flying'' photonic qubits. We describe work using mainly quasi-phase-matched nonlinear crystals to generate beams of entangled photon pairs, that are either encoded in polarization at near-visible wavelengths, or in time at optical fiber telecommunication wavelengths (1550 nm). The optical fiber is the medium used for transporting the qubits over a long distance, and it is therefore essential to couple the photons well into the fibers. By focusing the beams optimally, we have investigated how this problem can meet the requirement of creating photons of a narrow frequency bandwidth and a high photon flux. Furthermore, we have generated truly single photons that are heralded by an electrical signal. As a result of modifying the statistics of such sources we have been able to show the effect of photon antibunching. In two separate works, we have implemented a quantum key distribution system based on faint laser pulses at the telecom wavelength of 1550 nm, as well as protocols based on entanglement for performing authentication of key distribution in quantum cryptography.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. xv, 93 p.
Series
Trita-MVT, ISSN 0348-4467 ; 2006:1
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-616 (URN)91-7178-254-0 (ISBN)
Public defence
2006-02-23, Sal C1, Electrum, Isafjordsgatan 20-26, Kista, 10:00
Opponent
Supervisors
Note
QC 20100909Available from: 2006-02-10 Created: 2006-02-10 Last updated: 2010-09-09Bibliographically approved
2. Photonic Qubits for Quantum Communication: Exploiting photon-pair correlations; from theory to applications
Open this publication in new window or tab >>Photonic Qubits for Quantum Communication: Exploiting photon-pair correlations; from theory to applications
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

For any communication, the conveyed information must be carried by some physical system. If this system is a quantum system rather than a classical one, its behavior will be governed by the laws of quantum mechanics. Hence, the properties of quantum mechanics, such as superpositions and entanglement, are accessible, opening up new possibilities for transferring information. The exploration of these possibilities constitutes the field of quantum communication. The key ingredient in quantum communication is the qubit, a bit that can be in any superposition of 0 and 1, and that is carried by a quantum state. One possible physical realization of these quantum states is to use single photons. Hence, to explore the possibilities of optical quantum communication, photonic quantum states must be generated, transmitted, characterized, and detected with high precision. This thesis begins with the first of these steps: the implementation of single-photon sources generating photonic qubits. The sources are based on photon-pair generation in nonlinear crystals, and designed to be compatible with fiber optical communication systems. To ensure such a compatibility and to create a high-quality source, a theoretical analysis is made, optimizing the coupling of the photons into optical fibers. Based on the theoretical analysis, a heralded single-photon source and a two-crystal source of entangled photons-pairs are experimentally implemented. The source of entangled photons is further developed into a compact source with a narrow bandwidth compatible with standard telecommunication wavelength-division multiplexers, and even further developed to a more stable one-crystal source. The sources are to be used for quantum communication in general and quantum cryptography in particular. Specifically, a heralded single-photon source is implemented and then used for a full test of a decoy-state quantum cryptography protocol.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. xii, 79 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2008:13
Keyword
quantum communication, photon-pair sources, entanglement
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-4798 (URN)978-91-7415-005-6 (ISBN)
Public defence
2008-06-13, Sal D, Forum, KTH Kista, Isafjordsgatan 39, Kista, 10:00
Opponent
Supervisors
Note
QC 20100914Available from: 2008-06-04 Created: 2008-06-04 Last updated: 2010-09-14Bibliographically approved

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http://arxiv.org/PS_cache/arxiv/pdf/0706/0706.2985v1.pdf

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