Equivalent qubit dynamics under classical and quantum noise

We study the dynamics of quantum systems under classical and quantum noise, focusing on decoherence in qubit systems. Classical noise is described by a random process leading to a stochastic temporal evolution of a closed quantum system, whereas quantum noise originates from the coupling of the microscopic quantum system to its macroscopic environment. We derive deterministic master equations describing the average evolution of the quantum system under classical continuous-time Markovian noise and two sets of master equations under quantum noise. Strikingly, these three equations of motion are shown to be equivalent in the case of classical random telegraph noise and proper quantum environments. Hence fully quantum-mechanical models within the Born approximation can be mapped to a quantum system under classical noise. Furthermore, we apply the derived equations together with pulse optimization techniques to achieve high-fidelity one-qubit operations under random telegraph noise, and hence fight decoherence in these systems of great practical interest.Comment: 5 pages, 2 figures; converted to PRA format, added Fig. 2, corrected typo

Precision characterisation of two-qubit Hamiltonians via entanglement mapping

We show that the general Heisenberg Hamiltonian with non-uniform couplings can be characterised by mapping the entanglement it generates as a function of time. Identification of the Hamiltonian in this way is possible as the coefficients of each operator control the oscillation frequencies of the entanglement function. The number of measurements required to achieve a given precision in the Hamiltonian parameters is determined and an efficient measurement strategy designed. We derive the relationship between the number of measurements, the resulting precision and the ultimate discrete error probability generated by a systematic mis-characterisation, when implementing two-qubit gates for quantum computing.Comment: 6 Pages, 3 figure

Quantum circuits with many photons on a programmable nanophotonic chip

Growing interest in quantum computing for practical applications has led to a surge in the availability of programmable machines for executing quantum algorithms. Present day photonic quantum computers have been limited either to non-deterministic operation, low photon numbers and rates, or fixed random gate sequences. Here we introduce a full-stack hardware-software system for executing many-photon quantum circuits using integrated nanophotonics: a programmable chip, operating at room temperature and interfaced with a fully automated control system. It enables remote users to execute quantum algorithms requiring up to eight modes of strongly squeezed vacuum initialized as two-mode squeezed states in single temporal modes, a fully general and programmable four-mode interferometer, and genuine photon number-resolving readout on all outputs. Multi-photon detection events with photon numbers and rates exceeding any previous quantum optical demonstration on a programmable device are made possible by strong squeezing and high sampling rates. We verify the non-classicality of the device output, and use the platform to carry out proof-of-principle demonstrations of three quantum algorithms: Gaussian boson sampling, molecular vibronic spectra, and graph similarity

The curious compatibility of consensus, corporatism, and neoliberalism : The Finnish business community and the retasking of a corporatist welfare state

This article addresses the apparent paradox of simultaneous neoliberal change and welfare-statist, corporatist continuity by presenting an empirical case study of the advent of neoliberal ideas in Finland in the 1970s and 1980s. The article focuses on the attempts of a free-market think tank, EVA, and the employers’ association, STK, to advance policies such as economic deregulation, international competitiveness, welfare retrenchment, and active social and labour market policies through the neoliberal retasking of the corporatist Finnish welfare state. EVA and the STK utilised seemingly non-neoliberal means, that is an economic policy consensus and tripartite corporatist arrangements, and reformulated their content to better correspond with business interests. Instead of demolition, the outcome has been the redefinition and incremental transformation of the state from a provider of welfare to a promoter of competitiveness, productivity, and employment.Peer reviewe

Minimum Wages and Youth Employment: Evidence from the Finnish Retail Trade Sector

Following an agreement between the trade unions and the employer organisations, Finnish employers could pay less than the existing minimum wage for young workers between 1993 and 1995. We examine the effects of these minimum wage exceptions by comparing the changes in wages and employment of the groups whose minimum wages were reduced with simultaneous changes among slightly older workers for whom the minimum wage regulation was still binding. Our analysis is based on the payroll record data and minimum wage agreements from the retail trade sector over the period 1990-2005. We discover that average wages in the eligible group declined only modestly despite the fact that the excess supply of labour during high unemployment should make it relatively easy to attract workers even with low wages. The minimum wage exceptions had no positive effects on employment

Impact of inactivity and exercise on the vasculature in humans

The effects of inactivity and exercise training on established and novel cardiovascular risk factors are relatively modest and do not account for the impact of inactivity and exercise on vascular risk. We examine evidence that inactivity and exercise have direct effects on both vasculature function and structure in humans. Physical deconditioning is associated with enhanced vasoconstrictor tone and has profound and rapid effects on arterial remodelling in both large and smaller arteries. Evidence for an effect of deconditioning on vasodilator function is less consistent. Studies of the impact of exercise training suggest that both functional and structural remodelling adaptations occur and that the magnitude and time-course of these changes depends upon training duration and intensity and the vessel beds involved. Inactivity and exercise have direct “vascular deconditioning and conditioning” effects which likely modify cardiovascular risk