scholarly journals Towards joint reconstruction of noise and losses in quantum channels

2016 ◽  
Vol 3 (1) ◽  
Author(s):  
F. Piacentini ◽  
A. Avella ◽  
P. Traina ◽  
L. Lolli ◽  
E. Taralli ◽  
...  
Keyword(s):  
Quantum Channel ◽  
Quantum Communication ◽  
Photon Number ◽  
Practical Implementation ◽  
Quantum Metrology ◽  
Quantum Channels ◽  
Transmission Losses ◽  
Single Measurement ◽  
Joint Reconstruction

AbstractThe calibration of a quantum channel, i.e. the determination of the transmission losses affecting it, is definitely one of the principal objectives in both the quantum communication and quantum metrology frameworks. Another task of the utmost relevance is the identification, e.g. by extracting its photon number distribution, of the noise potentially present in the channel.Here we present a protocol, based on the response of a photon-number-resolving detector at different quantum efficiencies, able to accomplish both of these tasks at once, providing with a single measurement an estimate of the transmission losses as well as the photon statistics of the noise present in the exploited quantum channel.We show and discuss the experimental results obtained in the practical implementation of such protocol, with different kinds and levels of noise.

Performance characterization of Pauli channels assisted by indefinite causal order and post-measurement

2020 ◽  
Vol 20 (15&16) ◽  
pp. 1261-1280
Author(s):  
Francisco Delgado ◽  
Carlos Cardoso-Isidoro
Keyword(s):  
Quantum Channel ◽  
Communication Channel ◽  
Quantum Communication ◽  
Quantum Channels ◽  
Causal Order ◽  
Combined Process ◽  
Performance Characterization ◽  
Output State ◽  
Transmission Of Information

Indefinite causal order has introduced disruptive procedures to improve the fidelity of quantum communication by introducing the superposition of { orders} on a set of quantum channels. It has been applied to several well characterized quantum channels as depolarizing, dephasing and teleportation. This work analyses the behavior of a parametric quantum channel for single qubits expressed in the form of Pauli channels. Combinatorics lets to obtain affordable formulas for the analysis of the output state of the channel when it goes through a certain imperfect quantum communication channel when it is deployed as a redundant application of it under indefinite causal order. In addition, the process exploits post-measurement on the associated control to select certain components of transmission. Then, the fidelity of such outputs is analysed to characterize the generic channel in terms of its parameters. As a result, we get notable enhancement in the transmission of information for well characterized channels due to the combined process: indefinite causal order plus post-measurement.

ON THE SECURITY OF DECOHERENCE-FREE SUBSPACES AND SUBSYSTEMS FOR CLASSICAL INFORMATION CONVEYING THROUGH QUANTUM CHANNELS

2013 ◽  
Vol 11 (02) ◽  
pp. 1350022
Author(s):  
ELLOÁ B. GUEDES ◽  
FRANCISCO M. DE ASSIS
Keyword(s):  
Quantum Information ◽  
Communication Systems ◽  
Quantum Communication ◽  
Quantum Information Processing ◽  
Information Leakage ◽  
Practical Implementation ◽  
Quantum Channels ◽  
Quantum Properties ◽  
Message Exchange ◽  
Decoherence Free Subspaces

Decoherence is one of the main obstacles in quantum information processing. In cryptographic scenarios, in particular, decoherence is not only responsible for the loss of the quantum properties but also for information leakage out to a wiretapper. Given that decoherence must be fought in real-world quantum communication systems, we present a scheme, using decoherence-free subspaces and subsystems, to perform secure classical communications through noisy quantum channels. Using quantum information and wiretap theories, we establish a proof of unconditional security of our scheme. We illustrate our proposal with a non-trivial example and discuss some of its impacts on already existing quantum secure message exchange protocols. Furthermore, we present some up-to-date technologies that can be used for practical implementation of the scheme proposed.

scholarly journals On the one-shot zero-error classical capacity of classical-quantum channels assisted by quantum non-signalling correlations

2017 ◽  
Vol 17 (5&6) ◽  
pp. 380-398
Author(s):  
Ching-Yi Lai ◽  
Runyao Duan
Keyword(s):  
Quantum Channel ◽  
Quantum Communication ◽  
Semidefinite Program ◽  
Circulant Graph ◽  
Quantum Channels ◽  
Kraus Operator ◽  
Cyclotomic Cosets ◽  
Classical Capacity ◽  
Classical Quantum ◽  
The One

Duan and Winter studied the one-shot zero-error classical capacity of a quantum channel assisted by quantum non-signalling correlations, and formulated this problem as a semidefinite program depending only on the Kraus operator space of the channel. For the class of classical-quantum channels, they showed that the asymptotic zero-error classical capacity assisted by quantum non-signalling correlations, minimized over all classicalquantum channels with a confusability graph G, is exactly log ϑ(G), where ϑ(G) is the celebrated Lov´asz theta function. In this paper, we show that the one-shot capacity for a classical-quantum channel, induced from a circulant graph G defined by equal-sized cyclotomic cosets, is logbϑ(G)c, which further implies that its asymptotic capacity is log ϑ(G). This type of graphs include the cycle graphs of odd length, the Paley graphs of prime vertices, and the cubit residue graphs of prime vertices. Examples of other graphs are also discussed. This gives Lov´asz ϑ function another operational meaning in zero-error classical-quantum communication.

scholarly journals Security of direct communication quantum channel with feedback

2015 ◽  
Vol 13 (08) ◽  
pp. 1550062
Author(s):  
Constantin V. Usenko
Keyword(s):  
Density Matrix ◽  
Quantum Channel ◽  
Carrier Density ◽  
Indirect Method ◽  
Unconditional Security ◽  
Quantum Channels ◽  
Direct Communication ◽  
Average Information ◽  
Incompatible Observables

In the direct communication quantum channels, the authorized recipient (Bob) and the non-authorized recipient (Eve) have different abilities for verification of received information. Bob can apply the feedback to commit the sender (Alice) to perform verification. Eve has to use for verification an indirect method based on the measurement of a set of incompatible observables enough for determination of the coding basis used by Alice. In the protocol of direct communication, regular modification of coding basis and masking it with an equilibrium in average information carrier density matrix prevents reconstruction of coding basis by the results of Eve’s measurements of an arbitrary set of observables. This provides unconditional security of the channel.

scholarly journals Fundamental limitations on distillation of quantum channel resources

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Bartosz Regula ◽  
Ryuji Takagi
Keyword(s):  
Lower Bounds ◽  
Quantum Channel ◽  
Quantum Communication ◽  
Fault Tolerant ◽  
State Of The Art ◽  
Quantum Systems ◽  
Noisy Channels ◽  
General Transformation ◽  
Fundamental Limitations ◽  
Strong Converse

AbstractQuantum channels underlie the dynamics of quantum systems, but in many practical settings it is the channels themselves that require processing. We establish universal limitations on the processing of both quantum states and channels, expressed in the form of no-go theorems and quantitative bounds for the manipulation of general quantum channel resources under the most general transformation protocols. Focusing on the class of distillation tasks — which can be understood either as the purification of noisy channels into unitary ones, or the extraction of state-based resources from channels — we develop fundamental restrictions on the error incurred in such transformations, and comprehensive lower bounds for the overhead of any distillation protocol. In the asymptotic setting, our results yield broadly applicable bounds for rates of distillation. We demonstrate our results through applications to fault-tolerant quantum computation, where we obtain state-of-the-art lower bounds for the overhead cost of magic state distillation, as well as to quantum communication, where we recover a number of strong converse bounds for quantum channel capacity.

scholarly journals Optimal teleportation via noisy quantum channels without additional qubit resources

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Dong-Gil Im ◽  
Chung-Hyun Lee ◽  
Yosep Kim ◽  
Hyunchul Nha ◽  
M. S. Kim ◽  
...  
Keyword(s):  
Quantum Computing ◽  
Quantum Teleportation ◽  
Quantum Communication ◽  
Quantum Noise ◽  
Single Copy ◽  
Entangled State ◽  
Quantum Network ◽  
Quantum Channels ◽  
Maximally Entangled State ◽  
Near Term

AbstractQuantum teleportation exemplifies how the transmission of quantum information starkly differs from that of classical information and serves as a key protocol for quantum communication and quantum computing. While an ideal teleportation protocol requires noiseless quantum channels to share a pure maximally entangled state, the reality is that shared entanglement is often severely degraded due to various decoherence mechanisms. Although the quantum noise induced by the decoherence is indeed a major obstacle to realizing a near-term quantum network or processor with a limited number of qubits, the methodologies considered thus far to address this issue are resource-intensive. Here, we demonstrate a protocol that allows optimal quantum teleportation via noisy quantum channels without additional qubit resources. By analyzing teleportation in the framework of generalized quantum measurement, we optimize the teleportation protocol for noisy quantum channels. In particular, we experimentally demonstrate that our protocol enables to teleport an unknown qubit even via a single copy of an entangled state under strong decoherence that would otherwise preclude any quantum operation. Our work provides a useful methodology for practically coping with decoherence with a limited number of qubits and paves the way for realizing noisy intermediate-scale quantum computing and quantum communication.

Evaluation of eavesdropping error-rates in higher-dimensional QKD system implemented using dynamic spatial modes

2021 ◽  
Author(s):  
Muhammad Kamran ◽  
Tahir Malik ◽  
Muhammad Mubashir Khan
Keyword(s):  
Error Rate ◽  
Photon Number ◽  
Error Rates ◽  
Security And Privacy ◽  
Practical Implementation ◽  
Secret Key ◽  
Decoy State ◽  
Rate Analysis ◽  
Higher Dimensional ◽  
Spatial Modes

Secure exchange of cryptographic keys is extremely important for any communication system where security and privacy of data is desirable. Although classical cryptographic algorithms provide computationally secure methods for secret key exchange, quantum key distribution (QKD) provides an extraordinary means to this end by guaranteeing unconditional security. Any malicious interception of communication by a man-in-the-middle on a QKD link immediately alerts sender and receiver by introducing an unavoidable error-rate. Higher-dimensional QKD protocols such as KMB09 exhibit higher eavesdropping error-rates with improved intrusion detection but their practical implementation is still awaited. In this paper, we present the design and implementation of KMB09 protocol using Laguerre–Gaussian orbital angular momentum to demonstrate and highlight the advantages of using dynamic spatial modes in QKD system. A complete error-rate analysis of KMB09 protocol implementation is presented with two different types of eavesdropping error-rates. Furthermore, we also demonstrate the decoy state method to show the robustness of the protocol against photon-number-splitting attack.

Enzymes and Their Forms Used in Detection of Organophosphorus Compounds

2021 ◽  
pp. 22-41
Keyword(s):  
Organophosphorus Compounds ◽  
Degradation Products ◽  
Rapid Development ◽  
Hydrolytic Enzymes ◽  
Immobilized Enzymes ◽  
Amino Acid Sequences ◽  
Practical Implementation ◽  
Scientific Results ◽  
Physical And Chemical

Еnzymes are able to effectively interact with various organophosphorus compounds (OPC), entering into (bio)chemical reactions with them. Changes in the initial activity of enzymes as a result of their inhibition by OPC, the formation of OPC degradation products under the action of hydrolytic enzymes, etc. can be determined using different physical and chemical methods and used in bioanalytic systems to determine the concentrations of OPC. The purpose of the review is to analyze the main scientific results achieved over the past 10 years in the development of analytical systems based on enzymes intended for the determination of OPC. It is shown in the article, that the requirements for the sensitivity of biosensors are based on the norms of the content of the analyzed substances detected in/at the objects of mandatory control. The cholinesterases compose a basis for the development of the largest number of ultra-sensitive biosensors, although other enzymes can be successfully used as a biosensitive element. The most technologically advanced solution that is close to the practical implementation seems to be bioanalytical systems using immobilized enzymes. Improving the detection limits of the OPC can be achieved by using nanoobjects together with modern methods of signal transducers, for example, with nanomechanical detectors and signal converters. This combination of technical solutions ensures the sensitivity of the OPC analysis up to pg/l. At present, «reagentless» systems have received significant development, which have become the basis for the production of a large number of commercially available strips for the express determination of OPC. Modern demands stimulate the rapid development of portable and, especially, wearable biosensors that can be attached to various surfaces, including a clothing. The progress in the development of affine amino acid sequences, in the future, will allow the creation of enzyme biosensors on any surface.

scholarly journals Probabilistic Resumable Quantum Teleportation of a Two-Qubit Entangled State

Entropy ◽  
2019 ◽  
Vol 21 (4) ◽  
pp. 352 ◽  
Author(s):  
Zhan-Yun Wang ◽  
Yi-Tao Gou ◽  
Jin-Xing Hou ◽  
Li-Ke Cao ◽  
Xiao-Hui Wang
Keyword(s):  
Quantum Channel ◽  
Quantum Teleportation ◽  
The State ◽  
Entangled States ◽  
Entangled State ◽  
Quantum Channels ◽  
Unknown State ◽  
Optimal Probability

We explicitly present a generalized quantum teleportation of a two-qubit entangled state protocol, which uses two pairs of partially entangled particles as quantum channel. We verify that the optimal probability of successful teleportation is determined by the smallest superposition coefficient of these partially entangled particles. However, the two-qubit entangled state to be teleported will be destroyed if teleportation fails. To solve this problem, we show a more sophisticated probabilistic resumable quantum teleportation scheme of a two-qubit entangled state, where the state to be teleported can be recovered by the sender when teleportation fails. Thus the information of the unknown state is retained during the process. Accordingly, we can repeat the teleportion process as many times as one has available quantum channels. Therefore, the quantum channels with weak entanglement can also be used to teleport unknown two-qubit entangled states successfully with a high number of repetitions, and for channels with strong entanglement only a small number of repetitions are required to guarantee successful teleportation.

New Methodology for the Determination of the Vertical Center of Gravity of In-Service Semisubmersibles: Proposal and Numerical Assessment

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Ivan N. Porciuncula ◽  
Claudio A. Rodríguez ◽  
Paulo T. T. Esperança
Keyword(s):  
Accurate Determination ◽  
Center Of Gravity ◽  
Practical Implementation ◽  
Numerical Assessment ◽  
Neutral Equilibrium ◽  
Inclination Angles ◽  
Numerical Tools ◽  
The Stability ◽  
Metacentric Height

Along its lifetime, an offshore unit is subjected to several equipment interventions. These modifications may include large conversions in loco that usually are not adequately documented. Hence, the accurate determination of the platform's center of gravity (KG) is not possible. For vessels with low metacentric height (GM), such as semisubmersibles, Classification Societies penalize the platform's KG, inhibiting the installation of new equipment until an accurate measurement of KG is provided, i.e., until an updated inclining test is performed. For an operating semisubmersible, the execution of this type of test is not an alternative because it implies in removing the vessel from its in-service location to sheltered waters. Relatively recently, some methods have been proposed for the estimation of KG for in-service vessels. However, as all of the methods depend on accurate measurements of inclination angles and, eventually, on numerical tools for the simulation of vessel dynamics onboard, they are not straightforward for practical implementation. The objective of the paper is to present a practical methodology for the experimental determination of KG, without the need of accurate measurements of inclinations and/or complex numerical simulations, but based on actual operations that can be performed onboard. Indeed, the proposed methodology relies on the search, identification, and execution of a neutral equilibrium condition where, for instance, KG = KM. The method is exemplified using actual data of a typical semisubmersible. The paper also numerically explores and discusses the stability of the platform under various conditions with unstable initial GM, as well as the effect of mooring and risers.

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