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Concept# Quantum information science

Summary

Quantum information science is a field that combines the principles of quantum mechanics with information science to study the processing, analysis, and transmission of information. It covers both theoretical and experimental aspects of quantum physics, including the limits of what can be achieved with quantum information. The term quantum information theory is sometimes used, but it does not include experimental research and can be confused with a subfield of quantum information science that deals with the processing of quantum information.
Quantum teleportation, entanglement and the manufacturing of quantum computers depend on a comprehensive understanding of quantum physics and engineering. Google and IBM have invested significantly in quantum computer hardware research, leading to significant progress in manufacturing quantum computers since the 2010s. Currently, it is possible to create a quantum computer with over 100 qubits, but the error rate is high due to the lack of suitable materials for quantum computer manufacturing. Majorana fermions may be a crucial missing material.
Quantum cryptography devices are now available for commercial use. The one time pad, a cipher used by spies during the Cold War, uses a sequence of random keys for encryption. These keys can be securely exchanged using quantum entangled particle pairs, as the principles of the no-cloning theorem and wave function collapse ensure the secure exchange of the random keys. The development of devices that can transmit quantum entangled particles is a significant scientific and engineering goal.
Qiskit, Cirq and Q Sharp are popular quantum programming languages. Additional programming languages for quantum computers are needed, as well as a larger community of competent quantum programmers. To this end, additional learning resources are needed, since there are many fundamental differences in quantum programming which limits the amount of skills that can be carried over from traditional programming.

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Related publications (18)

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Related units (4)

PHYS-641: Quantum Computing

After introducing the foundations of classical and quantum information theory, and quantum measurement, the course will address the theory and practice of digital quantum computing, covering fundament

COM-309: Introduction to quantum information processing

Information is processed in physical devices. In the quantum regime the concept of classical bit is replaced by the quantum bit. We introduce quantum principles, and then quantum communications, key d

COM-611: Quantum Information Theory and Computation

Today one is able to manipulate matter at the nanoscale were quantum behavior becomes important and possibly information processing will have to take into account laws of quantum physics. We introduce

Quantum channel

In quantum information theory, a quantum channel is a communication channel which can transmit quantum information, as well as classical information. An example of quantum information is the state of a qubit. An example of classical information is a text document transmitted over the Internet. More formally, quantum channels are completely positive (CP) trace-preserving maps between spaces of operators. In other words, a quantum channel is just a quantum operation viewed not merely as the reduced dynamics of a system but as a pipeline intended to carry quantum information.

Quantum information science

Quantum information science is a field that combines the principles of quantum mechanics with information science to study the processing, analysis, and transmission of information. It covers both theoretical and experimental aspects of quantum physics, including the limits of what can be achieved with quantum information. The term quantum information theory is sometimes used, but it does not include experimental research and can be confused with a subfield of quantum information science that deals with the processing of quantum information.

Quantum key distribution

Quantum key distribution (QKD) is a secure communication method that implements a cryptographic protocol involving components of quantum mechanics. It enables two parties to produce a shared random secret key known only to them, which then can be used to encrypt and decrypt messages. The process of quantum key distribution is not to be confused with quantum cryptography, as it is the best-known example of a quantum-cryptographic task.

The exploration of open quantum many-body systems -systems of microscopic size exhibiting quantum coherence and interacting with their surrounding- has emerged as a key research area over the last years. The recent advances in controlling and preserving quantum coherence at the level of a single particle, developed in a wide variety of physical platforms, have been a major driving force in this field. The driven dissipative nature is a common characteristic of a wide class of modern experimental platforms in quantum science and technology, such as photonic systems, ultracold atoms, optomechanical systems, or superconducting circuits. The interplay between the coherent quantum dynamics and dissipation in open quantum systems leads to a wide range of novel out-of-equilibrium behaviours. Among them, the emergence in these systems of dynamical phases with novel broken symmetries, topological phases and the occurrence of dissipative phase transitions are of particular interest. This thesis aims at establishing a theoretical framework to engineer, characterize and control nonclassical states of light in photonic quantum optical networks in different regimes. The emphasis is put on its implementation, in particular with respect to integration and scalability in photonic platforms. In this thesis, we tackle some interesting aspects arising in the study of the dynamics of driven dissipative coupled nonlinear optical resonators. In that context, we consider the dynamics of two coupled nonlinear photonic cavities in the presence of inhomogeneous coherent driving and local dissipations using the Lindblad master equation formalism.We show that this simple open quantum many-body system can be subject to dynamical instabilities. In particular, our analysis shows that this system presents highly nonclassical properties and its dynamics exhibits dissipative Kerr solitons (DKSs), characterized by the robustness of its specific temporal or spatial waveform during propagation.In a second step, our intuition gained from this system composed of only few degrees of freedom is expanded to the study of systems of bigger size. In particular, we study DKSs originating from the parametric gain in Kerr microresonators. While DKSs are usually described using a classical mean-field approach, our work proposes a quantum-mechanical model formulated in terms of the truncated Wigner formalism. This analysis is motivated by the fact that technological implementations push towards the realization of DKSs in miniaturized integrated systems. These are operating at low power, a regime where quantum effects are expected to be relevant. Using the tools provided by the theory of open quantum systems, we propose a detailed investigation of the impact of quantum fluctuations on the spectral and dynamical properties of DKSs. We show that the quantum fluctuations arising from losses engender a finite lifetime to the soliton, and demonstrate that DKSs correspond to a specific class of dissipative time crystals.

The enormous advancements in the ability to detect and manipulate single quantum states have lead to the emerging field of quantum technologies. Among these, quantum computation is the most far-reaching and challenging, aiming to solve problems that the classic computers could never address because of the exponential scaling, while quantum sensing exploits the ability to address single quantum states to realize ultra-sensitive and precise detectors. Defect centers in semiconductors play a primary role in these fields. The possibility to store information in the spin of their ground state, manipulate it through microwaves, and read it optically allows to use them as qubits. In addition, the very sharp dependence of their properties on temperature, strain and magnetic fields makes them very promising quantum sensors. In this Thesis we aim at contributing to the progress of quantum technologies both at the hardware and software level. From a hardware point of view, we study a key property of defect centers in semiconductors, the phonon-assisted luminescence, which can be measured to perform the readout of the information stored in a quantum bit, or to detect temperature variations. We predict the luminescence and study the exciton-phonon couplings within a rigorous many-body perturbation theory framework,an analysis that has never been performed for defect centers.In particular, we study the optical emission of the negatively-charged boron vacancy in 2D hexagonal boron nitride, which currently stands out among defect centers in 2D materials thanks to its promise for applications in quantum information and quantum sensing. We show that phonons are responsible for the observed luminescence, which otherwise would be dark due to symmetry. We also show that the symmetry breaking induced by the static Jahn-Teller effect is not able to describe the presence of the experimentally observed peak at 1.5 eV.The knowledge of the coupling between electrons and phonons is fundamental for the accurate prediction of all the features of the photoluminescence spectrum. However, the large number of atoms in a defect supercell hinders the possibility use density functional perturbation theory to study this coupling. In this work we present a finite-differences technique to calculate the electron-phonon matrix elements, which exploits the symmetries of the defect in such a way to use the very same set of displacement needed for the calculation of phonons. The computation of electron-phonon coupling thus becomes a simple post-processing of the finite-differences phonons calculation. On the quantum software side, we propose an improved quantum algorithm to calculate the Green's function through real-time propagation, and use it to compute the retarded Green's function for the 2-, 3- and 4-site Hubbard models. This novel protocol significantly reduces the number of controlled operations when compared to those previously suggested in literature. Such reduction is quite remarkable when considering the 2-site Hubbard model, for which we show that it is possible to obtain the exact time propagation of the $\ket{N\pm 1}$ states by exponentiating one single Pauli component of the Hamiltonian, allowing us to perform the calculations on an actual superconducting quantum processor.

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This work presents a novel InGaAs/InP SPAD structure fabricated using a selective area growth (SAG) method. The surface topography of the selectively grown film deposited within the 70 mu m diffusion apertures is used to engineer the Zn diffusion profile to suppress premature edge breakdown. The device achieves a highly uniform active area without the need for shallow diffused guard ring (GR) regions that are inherent in standard InGaAs/InP SPADs. We have obtained 33% and 43% photon detection probability (PDP) at 1550 nm, with 5 V and 7 V excess bias, respectively. These measurements were performed at 300 K and 225 K. The dark count rate (DCR) per unit area at room temperature and at 5 V excess bias is 430 cps/mu m(2) and it decreases to 5 cps/mu m(2) at 225 K. Timing jitter is measured with passive quenching at 1550nm as 149 ps at full-width-at-half-maximum (FWHM), (300 K, 5 V excess bias). The proposed technology is suitable for a number of applications, including optical time-domain reflectometry (OTDR), quantum information, and light detection and ranging (LiDAR).

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Explores quantum entropy in Markov chains and Bell states, emphasizing entanglement.

Quantum Correction Codes 4CS-308: Introduction to quantum computation

Explains quantum correction codes using two classic codes to correct errors, focusing on goal flips and headlight flips.