Intrinsic quarks and heavy flavour production

A model is constructed for the diffractive production of heavy flavours in hadron-hadron interactions, based on the presence of an intrinsic heavy quark component in the hadron wavefunction. It requires three ingredients; the heavy quark content of the initial hadron, the probability that these heavy quarks are scattered, and the probability that they form heavy flavoured hadrons afterwards. The initial heavy quark distributions are calculated, using lowest order perturbative QCD, starting from the valence constituent quark distributions, and compared with deep inelastic charm production data. The valence distributions are designed to reproduce the dimensional counting rules, and, via reciprocity, to be consistent with the heavy quark fragmentation functions. The light quark-hadron scattering cross-section is parametrized by Pomeron exchange, and extended to heavy quarks using the f-dominance hypothesis for the Pomeron- quark coupling. Dynamical and kinematical factors which control the rise of these cross-sections from threshold are built in. The validity of these ideas is tested against charm photo-production data, by using a vector dominance model for the photon-hadron scattering. The probability that the scattered quarks recombine to produce heavy flavoured hadrons is assumed to be given by the overlap of the initial distribution of quarks with the distribution in a heavy hadron. We compare the predictions of our model with strangeness and charm production data, and make predictions for bottom and top production. In particular, the magnitude of the leptonic signal to be expected from the decay of top quarks produced at the CERN pp-Collider is given. We conclude that all aspects of this model are consistent with present experimental data, and that the top quark should be observed at the Collider if its mass is around 35 GeV

Commutation simulator for open quantum dynamics

Recent progress in quantum simulation and algorithms has demonstrated a rapid expansion in capabilities. The search continues for new techniques and applications to exploit quantum advantage. Here we propose an innovative method to investigate directly the properties of a time-dependent density operator $\hat{\rho}(t)$. Using generalised quantum commutation simulators, we can directly compute the expectation value of the commutation relation and thus of the rate of change of $\hat{\rho}(t)$. The approach can be utilised as a quantum eigen-vector solver for the von Neumann equation and a decoherence investigator for the Lindblad equation, by using just the statistics of single-qubit measurements. A simple but important example is demonstrated in the single-qubit case and we discuss extension of the method for practical quantum simulation with many qubits, towards investigation of more realistic quantum systems.Comment: 11 pages and 2 figure

Generating and verifying graph states for fault-tolerant topological measurement-based quantum computing in 2D optical lattices

We propose two schemes for implementing graph states useful for fault-tolerant topological measurement-based quantum computation in 2D optical lattices. We show that bilayer cluster and surface code states can be created by global single-row and controlled-Z operations. The schemes benefit from the accessibility of atom addressing on 2D optical lattices and the existence of an efficient verification protocol which allows us to ensure the experimental feasibility of measuring the fidelity of the system against the ideal graph state. The simulation results show potential for a physical realization toward fault-tolerant measurement-based quantum computation against dephasing and unitary phase errors in optical lattices.Comment: 6 pages and 4 figures (minor changed

Generalized parity measurements

Measurements play an important role in quantum computing (QC), by either providing the nonlinearity required for two-qubit gates (linear optics QC), or by implementing a quantum algorithm using single-qubit measurements on a highly entangled initial state (cluster state QC). Parity measurements can be used as building blocks for preparing arbitrary stabilizer states, and, together with 1-qubit gates are universal for quantum computing. Here we generalize parity gates by using a higher dimensional (qudit) ancilla. This enables us to go beyond the stabilizer/graph state formalism and prepare other types of multi-particle entangled states. The generalized parity module introduced here can prepare in one-shot, heralded by the outcome of the ancilla, a large class of entangled states, including GHZ_n, W_n, Dicke states D_{n,k}, and, more generally, certain sums of Dicke states, like G_n states used in secret sharing. For W_n states it provides an exponential gain compared to linear optics based methods.Comment: 7 pages, 1 fig; updated to the published versio

Deterministic amplification of Schroedinger cat states in circuit quantum electrodynamics

We propose a dynamical scheme for deterministically amplifying photonic Schroedinger cat states based on a set of optimal state-transfers. The scheme can be implemented in strongly coupled qubit-cavity systems and is well suited to the capabilities of state of the art superconducting circuits. The ideal analytical scheme is compared with a full simulation of the open Jaynes-Cummings model with realistic device parameters. This amplification tool can be utilized for practical quantum information processing in non-classical continuous-variable states.Comment: A revised manuscript has 6 figure