641 research outputs found
Quantum information with Gaussian states
Quantum optical Gaussian states are a type of important robust quantum states
which are manipulatable by the existing technologies. So far, most of the
important quantum information experiments are done with such states, including
bright Gaussian light and weak Gaussian light. Extending the existing results
of quantum information with discrete quantum states to the case of continuous
variable quantum states is an interesting theoretical job. The quantum Gaussian
states play a central role in such a case. We review the properties and
applications of Gaussian states in quantum information with emphasis on the
fundamental concepts, the calculation techniques and the effects of
imperfections of the real-life experimental setups.
Topics here include the elementary properties of Gaussian states and relevant
quantum information device, entanglement-based quantum tasks such as quantum
teleportation, quantum cryptography with weak and strong Gaussian states and
the quantum channel capacity, mathematical theory of quantum entanglement and
state estimation for Gaussian states.Comment: 170 pages. Minors of the published version are corrected and listed
in the Acknowledgement part of this versio
Quantum cryptography: key distribution and beyond
Uniquely among the sciences, quantum cryptography has driven both
foundational research as well as practical real-life applications. We review
the progress of quantum cryptography in the last decade, covering quantum key
distribution and other applications.Comment: It's a review on quantum cryptography and it is not restricted to QK
The Security of Practical Quantum Key Distribution
Quantum key distribution (QKD) is the first quantum information task to reach
the level of mature technology, already fit for commercialization. It aims at
the creation of a secret key between authorized partners connected by a quantum
channel and a classical authenticated channel. The security of the key can in
principle be guaranteed without putting any restriction on the eavesdropper's
power.
The first two sections provide a concise up-to-date review of QKD, biased
toward the practical side. The rest of the paper presents the essential
theoretical tools that have been developed to assess the security of the main
experimental platforms (discrete variables, continuous variables and
distributed-phase-reference protocols).Comment: Identical to the published version, up to cosmetic editorial change
Continuous-variable quantum key distribution in fast fading channels
We investigate the performance of several continuous-variable quantum key distribution protocols in the presence of fading channels. These are lossy channels whose transmissivity changes according to a probability distribution. This is typical in communication scenarios where remote parties are connected by free-space links subject to atmospheric turbulence. In this work, we assume the worst-case scenario where an eavesdropper has full control of a fast fading process, so that she chooses the instantaneous transmissivity of a channel, while the remote parties can only detect the mean statistical process. In our study, we consider coherent-state protocols run in various configurations, including the one-way switching protocol in reverse reconciliation, the measurement-device-independent protocol in the symmetric configuration and a three-party measurement-device-independent network. We show that, regardless of the advantage given to the eavesdropper (full control of fading), these protocols can still achieve high rates
Practical security bounds against the Trojan-horse attack in quantum key distribution
In the quantum version of a Trojan-horse attack, photons are injected into
the optical modules of a quantum key distribution system in an attempt to read
information direct from the encoding devices. To stop the Trojan photons, the
use of passive optical components has been suggested. However, to date, there
is no quantitative bound that specifies such components in relation to the
security of the system. Here, we turn the Trojan-horse attack into an
information leakage problem. This allows us quantify the system security and
relate it to the specification of the optical elements. The analysis is
supported by the experimental characterization, within the operation regime, of
reflectivity and transmission of the optical components most relevant to
security.Comment: 18 pages, 11 figures. Some typos correcte
Quantum Cryptography: Key Distribution and Beyond
Uniquely among the sciences, quantum cryptography has driven both foundational research as well as practical real-life applications. We review the progress of quantum cryptography in the last decade, covering quantum key distribution and other applications.Quanta 2017; 6: 1–47
Controlling an actively-quenched single photon detector with bright light
We control using bright light an actively-quenched avalanche single-photon
detector. Actively-quenched detectors are commonly used for quantum key
distribution (QKD) in the visible and near-infrared range. This study shows
that these detectors are controllable by the same attack used to hack
passively-quenched and gated detectors. This demonstrates the generality of our
attack and its possible applicability to eavsdropping the full secret key of
all QKD systems using avalanche photodiodes (APDs). Moreover, the commercial
detector model we tested (PerkinElmer SPCM-AQR) exhibits two new blinding
mechanisms in addition to the previously observed thermal blinding of the APD,
namely: malfunctioning of the bias voltage control circuit, and overload of the
DC/DC converter biasing the APD. These two new technical loopholes found just
in one detector model suggest that this problem must be solved in general, by
incorporating generally imperfect detectors into the security proof for QKD.Comment: Expanded discussions, updated references, added a picture of
decapsulated APD, reformatted to single-column style. Accepted to Opt.
Express. 11 pages, 6 figure
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