arXiv subjects
Publications and source records attributed to Joanna Wiśniewska.
By a use of the Fredholm determinant theory, the unified quantum entropy notion has been extended to a case of infinite-dimensional systems. Some of the known (in the finite-dimensional case) basic properties of the introduced unified entropies have been extended to the case study. Certain numerical approaches for computing the proposed finite and infinite-dimensional entropies are being outlined as well.
The data classification task is broadly utilized in numerous fields of science and it may be realized by different known approaches (e.g. neural networks). However, in this work, quantum computations were harnessed to solve the problem. We take into consideration a quantum circuit which is based on the Variational Quantum Eigensolver (VQE) and so-called SWAP-Test what allows us to solve a classification problem connected with credit sales. More specifically, we cope with a decision problem of determining customer's reliability based on values of selected decision variables (e.g. generated turnover, history of cooperation). The classical data samples are converted into normalized quantum states. After this operation, samples may be processed by a circuit of quantum gates. The VQE approach allows training the parameters of a quantum circuit (so-called ansatz) to output pattern-states for each class. In the utilized data set, two classes may be observed -- cases with low and high credit risk. However, the VQE circuit differentiates more classes than two (introduces more detailed cases) and the final results are obtained with the use of aforementioned SWAP-Test. The elaborated solution is compact and requires only logarithmically increasing number of qubits (due to the exponential capacity of quantum registers). Because of the low complexity of the presented quantum circuit, it is possible to perform experiments on currently available quantum computers, including the Noisy Intermediate-Scale Quantum (NISQ) devices. This type of devices, despite the presence of noise, is capable of solving the task analyzed in this work. All calculations, simulations, plots, and comparisons were implemented and conduced in the Python language environment. Source codes for each example of quantum classification can be found in the source code repository.
The Quantum Trajectories Method (QTM) is one of {the} frequently used methods for studying open quantum systems. { The main idea of this method is {the} evolution of wave functions which {describe the system (as functions of time). Then,} so-called quantum jumps are applied at {a} randomly selected point in time. {The} obtained system state is called as a trajectory. After averaging many single trajectories{,} we obtain the approximation of the behavior of {a} quantum system.} {This fact also allows} us to use parallel computation methods. In the article{,} we discuss the QTM package which is supported by the MPI technology. Using MPI allowed {utilizing} the parallel computing for calculating the trajectories and averaging them -- as the effect of these actions{,} the time {taken by} calculations is shorter. In spite of using the C++ programming language, the presented solution is easy to utilize and does not need any advanced programming techniques. At the same time{,} it offers a higher performance than other packages realizing the QTM. It is especially important in the case of harder computational tasks{,} and the use of MPI allows {improving the} performance of particular problems which can be solved in the field of open quantum systems.
We suppose that a structure working as a quantum switch will be a significant element of future networks realizing transmissions of quantum information. In this chapter we analyze a process of switch's operating -- especially in systems with a noise presence. The noise is caused by a phenomenon of quantum decoherence, i.e. distorting of quantum states because of an environmental influence, and also by some imperfections of quantum gates' implementation. In the face of mentioned problems, the possibility of tracing the switch's behavior during its operating seems very important. To realize that we propose to utilize a Coherence measure which, as we present in this chapter, is sufficient to describe operating of the quantum switch and to verify correctness of this process. It should be also stressed that the value of Coherence measure may be estimated by a quantum circuit, designed especially for this purpose.
The quantum entanglement is considered as one of the most important notions of quantum computing. The entanglement is a feature of quantum systems and it is used as a basis for many quantum algorithms and protocols. In this paper we analyze the level of entanglement for the quantum switch, during its work. The level of entanglement during the correct operating may be compared with the situation when a noise is present in the analyzed system. The noise changes the level of quantum entanglement and we utilize this observation to evaluate if the switch works properly. We present the formulae describing the value of entanglement with use of the Concurrence measure and also the value of entropy. Both mentioned values may be utilized to detect the noise during the operating of quantum switch.
In this chapter a quantum communication protocol with use of repeaters is presented. The protocol is constructed for qudits i.e. the generalized quantum information units. One-dit teleportation is based on the generalized Pauli-Z (phase-flip) gate's correction. This approach avoids using Pauli-X and Hadamard gates unlike in other known protocols based on quantum repeaters which were constructed for qubits and qudits. It is also important to mention that the repeaters based on teleportation protocol, described in this chapter, allow a measurement in the standard base (what simplifies the measurement process) and the use of teleportation causes only Pauli-Z operational errors.
The quantum entanglement is an important feature of many protocols in the field of quantum computing. In this paper we evaluate a level of entanglement in short qutrit chains. This evaluation is carried out with use of the CCNR criterion and the concurrence measure. We also present some explicit formulae describing the values of CCNR criterion and concurrence for exemplary short spin chains. Utilizing the obtained results, we indicate that analyzing the level of entanglement allows to detect the noise or deviation in the transfer process, in comparison to the perfect transfer where only operation realizing transfer is present.
The issue of quantum states' transfer -- in particular, for so-called Perfect State Transfer (PST) -- in the networks represented by the spin chains seems to be one of the major concerns in quantum computing. Especially, in the context of future communication methods that can be used in broadly defined computer science. The chapter presents a definition of Hamiltonian describing the dynamics of quantum data transfer in one-dimensional spin chain, which is able to transfer the state of unknown qudits. The main part of the chapter is the discussion about possibility of entangled states' perfect transfer, in particular, for the generalized Bell states for qudits. One of the sections also contains the results of numerical experiments for the transmission of quantum entangled state in a noisy quantum channel.