Narrow Results

In this analysis, we analytically obtain the eigenvalue solutions of non-relativistic quantum particles interacting with Mie-type potential in a topological defect geometry. Afterward, we study the thermodynamic properties for the quantum system, such as the vibrational free energy, mean energy, entropy, and specific heat using the partition unction and analyze the effects of topological defect. Furthermore, we calculated the Shannon entropy for this quantum system, thus measuring the loss of information about the particle’s location. This measure of information reveals the influence of the topological parameter on the location of the particle and provides us with more detailed parameters for a possible experimental detection of these quantum particles.

We consider Markovian open quantum dynamics (MOQD) in the continuum. We show that, up to small-probability tails, the supports of quantum states evolving under such dynamics propagate with finite speed in any finite-energy subspace. More precisely, we prove that if the initial quantum state is localized in space, then any finite-energy part of the solution of the von Neumann–Lindblad equation is approximately localized inside an energy-dependent light cone. We also obtain an explicit upper bound for the slope of this light cone.

The free contraction norm (or the (t)-norm) was introduced by Belinschi, Collins and Nechita as a tool to compute the typical location of the collection of singular values associated to a random subspace of the tensor product of two Hilbert spaces. In turn, it was used again by them in order to obtain sharp bounds for the violation of the additivity of the minimum output entropy (MOE) for random quantum channels with Bell states. This free contraction norm, however, is difficult to compute explicitly. The purpose of this note is to give a good estimate for this norm. Our technique is based on results of super convergence in the context of free probability theory. As an application, we give a new, simple and conceptual proof of the violation of the additivity of the MOE.

Using a Hubbard–Stratonovich like decomposition technique, we implemented simulations for the quantum circuits of Simon's algorithm for the detection of the periodicity of a function and Shor's algorithm for the factoring of prime numbers on a classical computer. Our approach has the advantage that the dimension of the problem does not grow exponentially with the number of qubits.

One obstacle in the simulation of quantum circuits is the high dimension of the Hilbert space. Using auxiliary field decompositions known from many-particle simulation, we can transform the mathematical description of the quantum circuit into a combination low-dimensional product states which can be sampled using Monte Carlo techniques. We demonstrate the method using Simon's algorithm for the detection of the period of a function.

In 2002, Li presented an asymmetrical quantum key distribution protocol which utilizes the correlations of Einstein-Podolsky-Rosen (EPR) pairs to establish a session key between two participants. Li claimed that an eavesdropper Eve cannot prevent his existence from being found by participants. However, this study shows that the session key can be obtained by Eve without being detected.

A scheme for quantum state sharing (QSTS) of a one-particle state is proposed for a three-particle GHZ state utilized as a quantum channel. After the sender (Alice) makes Bell-state measurements (BM) on her particles, and the controller (Charlie) performs a computational basis measurement (CM), the recipient (Bob) only needs to carry out a unitary transformation of the classical information from the sender and the controller. Finally, the scheme is generalized to multiparty QSTS of a one-qubit state with n agents and an m-qubit state with n agents.

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.

In this paper, we investigate two different entanglement measures, the negativity and concurrence, in the case of pure and mixed states of two-qubit system basing on the spin coherent states. For two-qubit pure states, the negativity is the same as the concurrence. For mixed states, using a simplified expression of concurrence in Wootters' measure of entanglement, we write the bounds of Verstraete et al.¹ as a function of some new parameters and we compare the both measures for a class of mixed states.

Quantum key agreement (QKA) can generate a shared secret key which is equally negotiated by all the participants in the protocol. In most of the QKA protocols, all the participants require quantum capabilities. But the quantum devices are too expensive for participants. This paper proposes a mutual semi-quantum key agreement protocol which allows two parties (Alice and Bob) to negotiate a shared secret key equally. In the protocol, Alice can perform any quantum operation, but Bob is a classical participant which can only perform reflection, measurement and reorder operation. Even though Bob has fewer quantum resources, Alice and Bob have an equal contribution to the shared final key, no one can determine the shared key alone. In addition, we demonstrate the security of the proposed protocol. The analysis results show that the proposed protocol not only resists against some common attacks but also assures the fairness property. It is significant for communication participant without enough quantum devices to achieve quantum communication. The proposed protocol can be implemented with present quantum technologies.

Quantum cryptography was proposed as a counter to the capacity of quantum computers to break classical cryptosystems. A broad subclass of quantum cryptography, called quantum key distribution (QKD), relies on quantum mechanical process for secure distribution of the keys. Quantum channels are inherently noisy, and therefore these protocols will be susceptible to noise as well. In this paper, we study the performance of two QKD protocols — BB84 and E91 under amplitude damping error. We show that while E91 protocol loses its security immediately due to loss of entanglement, the performance of BB84 protocol reduces to random guessing with increasing time. Next, we consider the action of an Eve on the BB84 protocol under amplitude damping noise, who is restricted to guessing the outcome of the protocol only. Under this restriction, we show that Eve can still do better than random guessing when equipped with the characteristics of the noisy channel. Finally, we propose a modification of the BB84 protocol which retains the security of the original protocol, but ensures that Eve cannot get any advantage in guessing the outcome, even with complete channel information.

An extension of Cencov’s categorical description of classical inference theory to the domain of quantum systems is presented. It provides a novel categorical foundation to the theory of quantum information that embraces both classical and quantum information theories in a natural way, while also allowing to formalize the notion of quantum environment. A first application of these ideas is provided by extending the notion of statistical manifold to incorporate categories, and investigating a possible, uniparametric Cramer–Rao inequality in this setting.

A Schrödinger equation is solved for a cotangent hyperbolic potential using the elegant parametric Nikiforov–Uvarov method. The results obtained are used to calculate the Fisher information for position space and momentum space as well as the Shannon entropy for position space and momentum space at the ground state. The energies of the cotangent potential are observed to be fully bounded for different quantum states. The Fisher information satisfied the Fisher relation known as Cramer–Rao inequality for the Fisher product. Its result also obeyed the Heisenberg principle as its alternative for uncertainty measurement. However, the Shannon entropy only satisfied the Bialynick-Birula, Mycielski inequality for higher values of the screening parameter. Its relation to the Heisenberg principle failed as both the position space and the momentum space are parallel with high entropy squeezing. This potential has not been reported for any system to the best of our understanding.

I discuss fundamental limits placed on information and information processing by gravity. Such limits arise because both information and its processing require energy, while gravitational collapse (formation of a horizon or black hole) restricts the amount of energy allowed in a finite region. Specifically, I use a criterion for gravitational collapse called the hoop conjecture. Once the hoop conjecture is assumed a number of results can be obtained directly: the existence of a fundamental uncertainty in spatial distance of order the Planck length, bounds on information (entropy) in a finite region, and a bound on the rate of information processing in a finite region. In the final section I discuss some cosmological issues, related to the total amount of information in the universe, and note that almost all detailed aspects of the late universe are determined by the randomness of quantum outcomes. This paper is based on a talk presented at a 2007 Bellairs Research Institute (McGill University) workshop on black holes and quantum information.

We show that for every qubit of quantum information, there is a well-defined notion of "the amount of energy that carries it," because it is a conserved quantity. This generalizes to larger systems and any conserved quantities: the eigenvalue spectrum of conserved charges has to be preserved while transferring quantum information. It is possible to "apparently" violate these conservations by losing a small fraction of information, but that must invoke a specific process which requires a large scale coherence. We discuss its implication regarding the black hole information paradox.

The noncommutative Bianchi I curved space–time vierbeins and spin connections are derived. Moreover, the corresponding noncommutative Dirac equation as well as its solutions are presented. As an application within the quantum field theory approach using Bogoliubov transformations, the von Neumann fermion–antifermion pair creation quantum entanglement entropy is studied. It is shown that its behavior is strongly dependent on the value of the noncommutativity $\theta$ parameter, $k_{\perp }$-modes frequencies and the structure of the curved space–time. Various discussions of the obtained features are presented.

Informational dependence between statistical or quantum subsystems can be described with Fisher information matrix or Fubini-Study metric obtained from variations/shifts of the sample/configuration space coordinates. Using these (noncovariant) objects as macroscopic constraints, we consider statistical ensembles over the space of classical probability distributions (i.e. in statistical space) or quantum wave functions (i.e. in Hilbert space). The ensembles are covariantized using dual field theories with either complex scalar field (identified with complex wave functions) or real scalar field (identified with square roots of probabilities). We construct space–time ensembles for which an approximate Schrodinger dynamics is satisfied by the dual field (which we call infoton due to its informational origin) and argue that a full space–time covariance on the field theory side is dual to local computations on the information theory side. We define a fully covariant information-computation tensor and show that it must satisfy certain conservation equations.

Then we switch to a thermodynamic description of the quantum/statistical systems and argue that the (inverse of) space–time metric tensor is a conjugate thermodynamic variable to the ensemble-averaged information-computation tensor. In (local) equilibrium, the entropy production vanishes, and the metric is not dynamical, but away from the equilibrium the entropy production gives rise to an emergent dynamics of the metric. This dynamics can be described approximately by expanding the entropy production into products of generalized forces (derivatives of metric) and conjugate fluxes. Near equilibrium, these fluxes are given by an Onsager tensor contracted with generalized forces and on the grounds of time-reversal symmetry, the Onsager tensor is expected to be symmetric. We show that a particularly simple and highly symmetric form of the Onsager tensor gives rise to the Einstein–Hilbert term. This proves that general relativity is equivalent to a theory of nonequilibrium (thermo)dynamics of the metric, but the theory is expected to break down far away from equilibrium where the symmetries of the Onsager tensor are to be broken.

In this paper, we estimate the net information exchange between adjacent quantum subsystems holographically living on the boundary of $\mathrm{\text{AdS}}$ space–time. The information exchange is a real-time phenomenon and only after long-time interval it may get saturated. Normally, we prepare systems for small time intervals and measure the information exchange over finite interval only. We find that the information flow between entangled subsystems gets reduced if systems are in excited state whereas the ground state allows maximum information flow at any given time. Especially for ${\mathrm{\text{CFT}}}_2$ we exactly show that a rise in the entropy is detrimental to the information exchange by a quantum dot and vice-versa. We next observe that there is a reduction in circuit (CV) complexity too in the presence of excitations for small times.

Analyzing the phenomenon of deconfinement from a holographic point of view, it appears that the brane configuration in the bulk, corresponding to the confinement phase imposes a restriction on the strength of the holographic quantum error correction procedure. This restriction is partially removed when the transition to a deconfined phase occurs. The brane configurations corresponding to the bulk instantons are analyzed and it is shown that they cannot reach the region of the bulk that would ensure maximal error protection in the confinement phase, while keeping non-zero instanton size. In the deconfinement phase on the other side, we have a configuration that allows a higher degree of quantum error protection, still preventing the maximal protection allowed by the holographic principle. This suggests that the strength of quantum error correction codes in QCD systems is fundamentally limited both in confinement and deconfinement phases.

Following an alternative version of Grover's algorithm, we propose a scheme to read- in information in Mn₁₂ molecular magnets with the help of multi-frequency magnetic pulses in two separate steps: first to realize an intermediate state |Ψ(T₁)> and then to reach the state |Ψ(T₂)> to encode information. All controllable parameters are calculated to implement read-in of information, and the durations of magnetic pulses are less than the dephasing time of quantum states in Mn₁₂. It is also shown that all the states of information can be initialized back to the intermediate state.