scholarly journals Quantum communication with coherent states of light

2017 ◽  
Vol 375 (2099) ◽  
pp. 20160235 ◽  
Author(s):  
Imran Khan ◽  
Dominique Elser ◽  
Thomas Dirmeier ◽  
Christoph Marquardt ◽  
Gerd Leuchs
Keyword(s):  
Coherent States ◽  
Secure Communication ◽  
Communication Systems ◽  
Quantum Communication ◽  
Continuous Variable ◽  
Quantum States ◽  
Complexity Of Algorithms ◽  
Laser Systems ◽  
Quantum Technology ◽  
Photon States

Quantum communication offers long-term security especially, but not only, relevant to government and industrial users. It is worth noting that, for the first time in the history of cryptographic encoding, we are currently in the situation that secure communication can be based on the fundamental laws of physics (information theoretical security) rather than on algorithmic security relying on the complexity of algorithms, which is periodically endangered as standard computer technology advances. On a fundamental level, the security of quantum key distribution (QKD) relies on the non-orthogonality of the quantum states used. So even coherent states are well suited for this task, the quantum states that largely describe the light generated by laser systems. Depending on whether one uses detectors resolving single or multiple photon states or detectors measuring the field quadratures, one speaks of, respectively, a discrete- or a continuous-variable description. Continuous-variable QKD with coherent states uses a technology that is very similar to the one employed in classical coherent communication systems, the backbone of today’s Internet connections. Here, we review recent developments in this field in two connected regimes: (i) improving QKD equipment by implementing front-end telecom devices and (ii) research into satellite QKD for bridging long distances by building upon existing optical satellite links. This article is part of the themed issue ‘Quantum technology for the 21st century’.

scholarly journals Preparation of a superposition of squeezed coherent states of a cavity field via coupling to a superconducting charge qubit

2020 ◽  
Vol 16 ◽  
pp. 1
Author(s):  
Dagoberto S. Freitas
Keyword(s):  
Radiation Field ◽  
Quantum State ◽  
Coherent States ◽  
Unitary Transformation ◽  
Quantum Communication ◽  
Quantum States ◽  
Cavity Field ◽  
Nonclassical States ◽  
Charge Qubit ◽  
The Past

The generation of nonclassical states of a radiation field has become increasingly important in the past years given its various applications in quantum communication. It has been recently proposed a way to engineer quantum states using a SQUID charge qubit inside a cavity with a controllable interaction between the cavity field and the charge qubit. Since decoherence is known to affect quantum effects uninterruptedly and decoherence process are working even when the quantum state is being formed, therefore, is interesting to envisage processes through which quantum superpositions are generated as fast as possible. We succeed in linearizing the Hamiltonian of the system through the application of an appropriate unitary transformation and for certain values of the parameters involved, we show that it is possible to obtain specific Hamiltonians. In this work we will use this approach for preparing superposition of two squeezed coherent states.

scholarly journals Preparation of a superposition of squeezed coherent states of a cavity field via coupling to a superconducting charge qubit

2020 ◽  
Vol 16 ◽  
pp. 1-6
Author(s):  
Dagoberto S. Freitas
Keyword(s):  
Radiation Field ◽  
Quantum State ◽  
Coherent States ◽  
Unitary Transformation ◽  
Quantum Communication ◽  
Quantum States ◽  
Cavity Field ◽  
Nonclassical States ◽  
Charge Qubit ◽  
The Past

The generation of nonclassical states of a radiation field has become increasingly important in the past years given its various applications in quantum communication. It has been recently proposed a way to engineer quantum states using a SQUID charge qubit inside a cavity with a controllable interaction between the cavity field and the charge qubit. Since decoherence is known to affect quantum effects uninterruptedly and decoherence process are working even when the quantum state is being formed, therefore, is interesting to envisage processes through which quantum superpositions are generated as fast as possible. We succeed in linearizing the Hamiltonian of the system through the application of an appropriate unitary transformation and for certain values of the parameters involved, we show that it is possible to obtain specific Hamiltonians. In this work we will use this approach for preparing superposition of two squeezed coherent states.

scholarly journals Unidimensional Continuous-Variable Quantum Key Distribution with Untrusted Detection under Realistic Conditions

Entropy ◽  
2019 ◽  
Vol 21 (11) ◽  
pp. 1100 ◽  
Author(s):  
Luyu Huang ◽  
Yichen Zhang ◽  
Ziyang Chen ◽  
Song Yu
Keyword(s):  
Quantum Key Distribution ◽  
Coherent States ◽  
Secure Communication ◽  
Key Distribution ◽  
Continuous Variable ◽  
Third Party ◽  
Modulation Method ◽  
Secret Key ◽  
Long Distance ◽  
Quantum Key Distribution Protocol

A unidimensional continuous-variable quantum key distribution protocol with untrusted detection is proposed, where the two legitimate partners send unidimensional modulated or Gaussian-modulated coherent states to an untrusted third party, i.e., Charlie, to realize the measurement. Compared with the Gaussian-modulated coherent-state protocols, the unidimensional modulated protocols take the advantage of easy modulation, low cost, and only a small number of random numbers required. Security analysis shows that the proposed protocol cannot just defend all detectors side channels, but also achieve great performance under certain conditions. Specifically, three cases are discussed in detail, including using unidimensional modulated coherent states in Alice’s side, in Bob’s side, and in both sides under realistic conditions, respectively. Under the three conditions, we derive the expressions of the secret key rate and give the optimal gain parameters. It is found that the optimal performance of the protocol is achieved by using unidimensional modulated coherent states in both Alice’s and Bob’s side. The resulting protocol shows the potential for long-distance secure communication using the unidimensional quantum key distribution protocol with simple modulation method and untrusted detection under realistic conditions.

Some attacks on quantum-based cryptographic protocols

2005 ◽  
Vol 5 (1) ◽  
pp. 40-47
Author(s):  
H-K Lo ◽  
T-M Ko
Keyword(s):  
Coherent States ◽  
Secure Communication ◽  
Single Photon ◽  
Cryptographic Protocols ◽  
Original Design ◽  
Information Theoretic ◽  
Information Theoretic Security ◽  
Photon States ◽  
Lossy Channel ◽  
Known Plaintext Attack

Quantum-based cryptographic protocols are often said to enjoy security guaranteed by the fundamental laws of physics. However, even carefully designed quantum-based cryptographic schemes may be susceptible to subtle attacks that are outside the original design. As an example, we give attacks against a recently proposed ``secure communication using mesoscopic coherent states'', which employs mesoscopic states, rather than single-photon states. Our attacks can be used either as a known-plaintext attack or in the case where the plaintext has not been randomized. One of our attacks requires beamsplitters and the replacement of a lossy channel by a lossless one. It is successful provided that the original loss in the channel is so big that Eve can obtain $2^k$ copies of what Bob receives, where $k$ is the length of the seed key pre-shared by Alice and Bob. In addition, substantial improvements over such an exhaustive key search attack can be made, whenever a key is reused. Furthermore, we remark that, under the same assumption of a known or non-random plaintext, Grover's exhaustive key search attack can be applied directly to "secure communication using mesoscopic coherent states", whenever the channel loss is more than 50 percent. Therefore, as far as information-theoretic security is concerned, optically amplified signals necessarily degrade the security of the proposed scheme, when the plaintext is known or non-random. Our attacks apply even if the mesoscopic scheme is used only for key generation with a subsequent use of the key for one-time-pad encryption. Studying those attacks can help us to better define the risk models and parameter spaces in which quantum-based cryptographic schemes can operate securely. Finally, we remark that our attacks do not affect standard protocols such as Bennett-Brassard BB84 protocol or Bennett B92 protocol, which rely on single-photon signals.

SECURE DIRECT COMMUNICATION USING DETERMINISTIC BB84 PROTOCOL

2008 ◽  
Vol 19 (04) ◽  
pp. 625-635 ◽  
Author(s):  
TZONELIH HWANG ◽  
CHUAN-MING LI ◽  
NARN-YIH LEE
Keyword(s):  
Secure Communication ◽  
Quantum Communication ◽  
Single Photon ◽  
Quantum Channels ◽  
Direct Communication ◽  
Bb84 Protocol ◽  
Practical Applications ◽  
Single Qubit ◽  
Set Up ◽  
Photon States

This paper presents a deterministic BB84 (dBB84) protocol that not only inherits the unconditional security of the original BB84 protocol but also enables the receiver to deterministically measure and decode all qubits sent by the sender. The proposed dBB84 protocol is then extended to be a deterministic secure quantum communication (DSQC) protocol wherein the sender can securely transmit secret messages to the receiver via quantum channels and the receiver can read out the secret messages only after receiving an additional classical bit for each qubit from the sender. In contrast to the existing single-photon-based secure communication protocols, which require the sender to either prepare two-qubit photon states or to establish two-way quantum channels with the receiver, the newly proposed protocol requires the sender to prepare single-qubit photon states for message transmissions and only set up one-way quantum channels to the receiver. Therefore, the proposed protocol is very suitable and feasible in practical applications.

scholarly journals Feasibility of satellite-to-ground continuous-variable quantum key distribution

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Daniele Dequal ◽  
Luis Trigo Vidarte ◽  
Victor Roman Rodriguez ◽  
Giuseppe Vallone ◽  
Paolo Villoresi ◽  
...  
Keyword(s):  
Quantum Key Distribution ◽  
Secure Communication ◽  
Communication Systems ◽  
Channel Model ◽  
Finite Size ◽  
Key Distribution ◽  
Continuous Variable ◽  
Space Environment ◽  
Limiting Factor ◽  
Secret Key

AbstractEstablishing secure communication links at a global scale is a major potential application of quantum information science but also extremely challenging for the underlying technology. Although milestone experiments using satellite-to-ground links and exploiting singe-photon encoding for implementing quantum key distribution have shown recently that this goal is achievable, it is still necessary to further investigate practical solutions compatible with classical optical communication systems. Here, we examine the feasibility of establishing secret keys in a satellite-to-ground downlink configuration using continuous-variable encoding, which can be implemented using standard telecommunication components certified for space environment and able to operate at high symbol rates. Considering a realistic channel model and state-of-the-art technology, and exploiting an orbit subdivision technique for mitigating fluctuations in the transmission efficiency, we find positive secret key rates for a low-Earth-orbit scenario, whereas finite-size effects can be a limiting factor for higher orbits. Our analysis determines regions of values for important experimental parameters where secret key exchange is possible and can be used as a guideline for experimental efforts in this direction.

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