Transition Dynamics in Vintage Capital Models: Explaining the Postwar Catch-Up of Germany and Japan

We consider a neoclassical interpretation of Germany and Japan's rapid postwar growth that relies on a catch-up mechanism through capital accumulation where technology is embodied in new capital goods. Using a putty-clay model of production and investment, we are able to capture many of the key empirical properties of Germany and Japan's postwar transitions, including persistently high but declining rates of labor and total-factor productivity growth, a U-shaped response of the capital-output ratio, rising rates of investment and employment, and moderate rates of return to capital.

Optimal tracking for pairs of qubit states

In classical control theory, tracking refers to the ability to perform measurements and feedback on a classical system in order to enforce some desired dynamics. In this paper we investigate a simple version of quantum tracking, namely, we look at how to optimally transform the state of a single qubit into a given target state, when the system can be prepared in two different ways, and the target state depends on the choice of preparation. We propose a tracking strategy that is proved to be optimal for any input and target states. Applications in the context of state discrimination, state purification, state stabilization and state-dependent quantum cloning are presented, where existing optimality results are recovered and extended.Comment: 15 pages, 8 figures. Extensive revision of text, optimality results extended, other physical applications include

Efficient Parity Encoded Optical Quantum Computing

We present a linear optics quantum computation scheme with a greatly reduced cost in resources compared to KLM. The scheme makes use of elements from cluster state computation and achieves comparable resource usage to those schemes while retaining the circuit based approach of KLM

Encoding qubits into oscillators with atomic ensembles and squeezed light

The Gottesman-Kitaev-Preskill (GKP) encoding of a qubit within an oscillator provides a number of advantages when used in a fault-tolerant architecture for quantum computing, most notably that Gaussian operations suffice to implement all single- and two-qubit Clifford gates. The main drawback of the encoding is that the logical states themselves are challenging to produce. Here we present a method for generating optical GKP-encoded qubits by coupling an atomic ensemble to a squeezed state of light. Particular outcomes of a subsequent spin measurement of the ensemble herald successful generation of the resource state in the optical mode. We analyze the method in terms of the resources required (total spin and amount of squeezing) and the probability of success. We propose a physical implementation using a Faraday-based quantum non-demolition interaction.Comment: (v2) consistent with published version; (v1) 16 pages, 5 figure

Efficient Toffoli Gates Using Qudits

The simplest decomposition of a Toffoli gate acting on three qubits requires {\em five} 2-qubit gates. If we restrict ourselves to controlled-sign (or controlled-NOT) gates this number climbs to six. We show that the number of controlled-sign gates required to implement a Toffoli gate can be reduced to just {\em three} if one of the three quantum systems has a third state that is accessible during the computation, i.e. is actually a qutrit. Such a requirement is not unreasonable or even atypical since we often artificially enforce a qubit structure on multilevel quantums systems (eg. atoms, photonic polarization and spatial modes). We explore the implementation of these techniques in optical quantum processing and show that linear optical circuits could operate with much higher probabilities of success

Choice of Measurement Sets in Qubit Tomography

Optimal generalized measurements for state estimation are well understood. However, practical quantum state tomography is typically performed using a fixed set of projective measurements and the question of how to choose these measurements has been largely unexplored in the literature. In this work we develop theoretical asymptotic bounds for the average fidelity of pure qubit tomography using measurement sets whose axes correspond to vertices of Platonic solids. We also present complete simulations of maximum likelihood tomography for mixed qubit states using the Platonic solid measurements. We show that overcomplete measurement sets can be used to improve the accuracy of tomographic reconstructions.Comment: 13 Pages, 6 figure

Experiences of physical activity during pregnancy resulting from in vitro fertilisation: an interpretative phenomenological analysis

Objective To explore the qualitative experiences and decision-making processes surrounding physical activity (PA) for women who have undergone IVF treatment. Background Physical activity (PA) during pregnancy is safe for both mother and fetus in the majority of cases, including for women who have undergone in vitro fertilisation (IVF) treatment; however, there is a paucity of research into decision-making and PA in this population. Methods Eight women, who had undergone successful IVF treatment and were currently pregnant or had given birth within the last two years, participated in semi-structured interviews about their experiences of infertility and PA during pregnancy. Interview transcripts were analysed using interpretative phenomenological analysis. Results Three superordinate themes emerged from the data: ‘navigating away from childlessness and towards motherhood’, ‘negotiating a safe passage’, and ‘balancing the challenges of pregnancy with the needs of the self’. Ten subthemes indicated the processes adopted to navigate experiences of infertility, the IVF process, and subsequent decision-making about PA during pregnancy. Conclusion PA during pregnancy was experienced as a way to soothe the self and control the experience of pregnancy; however, this was mediated by concerns about safety and physical limitations on PA. Limitations of the study are considered, as well as implications for clinical practice and directions for future research