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Postdoctoral Fellow X-Ray Optics: PAUL SCHERRER INSTITUTE

brightrecruits jobs - Fri, 2017-12-08 17:33
€Competitive: PAUL SCHERRER INSTITUTE
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Research Associate in Computational Materials Chemistry: UNIVERSITY COLLEGE LONDON

brightrecruits jobs - Fri, 2017-12-08 17:12
£Excellent: UNIVERSITY COLLEGE LONDON
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Graduate Software Test Engineer - Python, S/W test, Cambridge, to 30k : ECM SELECTION

brightrecruits jobs - Fri, 2017-12-08 13:41
£25,000 to £30,000 per annum: ECM SELECTION
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Optics Researcher / Physicist : VECTOR RECRUITMENT LIMITED

brightrecruits jobs - Fri, 2017-12-08 13:16
£Attractive + Benefits package + Relocation package: VECTOR RECRUITMENT LIMITED
For more latest jobs and jobs in London & South East England visit brightrecruits.com
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Machine Learning Engineer - Medical Devices : VECTOR RECRUITMENT LIMITED

brightrecruits jobs - Fri, 2017-12-08 11:19
£Attractive + Benefits package + Share options: VECTOR RECRUITMENT LIMITED
For more latest jobs and jobs in East of England visit brightrecruits.com
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Strong quantum squeezing of mechanical resonator via parametric amplification and coherent feedback

Author(s): Xiang You, Zongyang Li, and Yongmin Li

A scheme to achieve strong quantum squeezing of a mechanical resonator in a membrane-in-the-middle optomechanical system is developed. To this end, simultaneous linear and nonlinear coupling between the mechanical resonator and the cavity modes is applied. A two-tone driving light field, comprising ...


[Phys. Rev. A 96, 063811] Published Fri Dec 08, 2017

Categories: Journals, Physics

Optical and microwave control of resonance fluorescence and squeezing spectra in a polar molecule

Author(s): M. A. Antón, S. Maede-Razavi, F. Carreño, I. Thanopulos, and E. Paspalakis

A two-level quantum emitter with broken inversion symmetry simultaneously driven by an optical field and a microwave field that couples to the permanent dipole's moment is presented. We focus to a situation where the angular frequency of the microwave field is chosen such that it closely matches the...


[Phys. Rev. A 96, 063812] Published Fri Dec 08, 2017

Categories: Journals, Physics

Demonstration of Two-Atom Entanglement with Ultrafast Optical Pulses

Author(s): J. D. Wong-Campos, S. A. Moses, K. G. Johnson, and C. Monroe

We demonstrate quantum entanglement of two trapped atomic ion qubits using a sequence of ultrafast laser pulses. Unlike previous demonstrations of entanglement mediated by the Coulomb interaction, this scheme does not require confinement to the Lamb-Dicke regime and can be less sensitive to ambient ...


[Phys. Rev. Lett. 119, 230501] Published Fri Dec 08, 2017

Categories: Journals, Physics

Focus: Liquid String Vibrations

APS Physics - Fri, 2017-12-08 11:00

Author(s): Michael Schirber

A liquid microchannel—the line where three soap films meet—vibrates like a string whose diameter shrinks as the shaking force increases.  


[Physics 10, 133] Published Fri Dec 08, 2017

Categories: Physics

Symmetric three-qubit-state invariants

PRA: Quantum information - Fri, 2017-12-08 11:00

Author(s): Alexander Meill and David A. Meyer

For pure symmetric three-qubit states there are only three algebraically independent entanglement measures; one choice is the pairwise concurrence C, the three-tangle τ, and the Kempe invariant κ. Using a canonical form for symmetric n-qubit states derived from their Majorana representation, we deri...


[Phys. Rev. A 96, 062310] Published Fri Dec 08, 2017

Categories: Journals, Physics

Majorana-based fermionic quantum computation. (arXiv:1712.02353v1 [quant-ph])

arXiv.org: Quantum Physics - Fri, 2017-12-08 09:45

Because Majorana zero modes store quantum information non-locally, they are protected from noise, and have been proposed as a building block for a quantum computer. We show how to use the same protection from noise to implement universal fermionic quantum computation. Our architecture requires only two Majoranas to encode a (fermionic) quantum degree of freedom, compared to alternative implementations which require a minimum of four Majoranas for a spin quantum degree of freedom. The fermionic degrees of freedom support both unitary coupled cluster variational quantum eigensolver and quantum phase estimation algorithms, proposed for quantum chemistry simulations. Because we avoid the Jordan-Wigner transformation, our scheme has a lower overhead for implementing both of these algorithms, and it allows to simulate a Trotterized Hubbard Hamiltonian in O(1) time. We finally demonstrate magic state distillation in our fermionic architecture, giving a universal set of topologically protected fermionic quantum gates.

Categories: Journals, Physics

Infrared Divergences and Quantum Coherence. (arXiv:1712.02355v1 [hep-th])

arXiv.org: Quantum Physics - Fri, 2017-12-08 09:45

In theories with long-range forces like QED or perturbative gravity, only rates that include emitted soft radiation are non-vanishing. Independently of detector resolution, finite observables can only be obtained after integrating over the IR-component of this radiation. This integration can lead to some loss of quantum coherence. In this note, however, we argue that it should in general not lead to full decoherence. Based on unitarity, we suggest a way to define non-vanishing off-diagonal pieces of the IR-finite density matrix. For this IR-finite density matrix, we estimate the dependence of the loss of quantum coherence, i.e. of its purity, on the scattering kinematics.

Categories: Journals, Physics

Semiclassical theory of the tunneling anomaly in partially spin-polarized compressible quantum Hall states. (arXiv:1712.02357v1 [cond-mat.str-el])

arXiv.org: Quantum Physics - Fri, 2017-12-08 09:45

Electron tunneling into a system with strong interactions is known to exhibit an anomaly, in which the tunneling conductance vanishes continuously at low energy due to many-body interactions. Recent measurements have probed this anomaly in a quantum Hall bilayer of the half-filled Landau level, and shown that the anomaly apparently gets stronger as the half-filled Landau level is increasingly spin polarized. Motivated by this result, we construct a semiclassical hydrodynamic theory of the tunneling anomaly in terms of the charge-spreading action associated with tunneling between two copies of the Halperin-Lee-Read state with partial spin polarization. This theory is complementary to our recent work (arXiv:1709.06091) where the electron spectral function was computed directly using an instanton-based approach. Our results show that the experimental observation cannot be understood within conventional theories of the tunneling anomaly, in which the spreading of the injected charge is driven by the mean-field Coulomb energy. However, we identify a qualitatively new regime, in which the mean-field Coulomb energy is effectively quenched and the tunneling anomaly is dominated by the finite compressibility of the composite Fermion liquid.

Categories: Journals, Physics

Adaptive weight estimator for quantum error correction. (arXiv:1712.02360v1 [quant-ph])

arXiv.org: Quantum Physics - Fri, 2017-12-08 09:45

Quantum error correction of a surface code or repetition code requires the pairwise matching of error events in a space-time graph of qubit measurements, such that the total weight of the matching is minimized. The input weights follow from a physical model of the error processes that affect the qubits. This approach becomes problematic if the system has sources of error that change over time. Here we show how the weights can be determined from the measured data in the absence of an error model. The resulting adaptive decoder performs well in a time-dependent environment, provided that the characteristic time scale $\tau_{\mathrm{env}}$ of the variations is greater than $\delta t/\bar{p}$, with $\delta t$ the duration of one error-correction cycle and $\bar{p}$ the typical error probability per qubit in one cycle.

Categories: Journals, Physics

Causal Asymmetry in a Quantum World. (arXiv:1712.02368v1 [quant-ph])

arXiv.org: Quantum Physics - Fri, 2017-12-08 09:45

Causal asymmetry is one of the great surprises in predictive modelling: the memory required to predictive the future differs from the memory required to retrodict the past. There is a privileged temporal direction for modelling a stochastic process where memory costs are minimal. Models operating in the other direction incur an unavoidable memory overhead. Here we show that this overhead can vanish when quantum models are allowed. Quantum models forced to run in the less natural temporal direction not only surpass their optimal classical counterparts, but also any classical model running in reverse time. This holds even when the memory overhead is unbounded, resulting in quantum models with unbounded memory advantage.

Categories: Journals, Physics

Recoverable Information and Emergent Conservation Laws in Fracton Stabilizer Codes. (arXiv:1712.02375v1 [quant-ph])

arXiv.org: Quantum Physics - Fri, 2017-12-08 09:45

We introduce a new quantity, that we term recoverable information, defined for stabilizer Hamiltonians. For such models, the recoverable information provides a measure of the topological information, as well as a physical interpretation, which is complementary to topological entanglement entropy. We discuss three different ways to calculate the recoverable information, and prove their equivalence. To demonstrate its utility, we compute recoverable information for fracton models using all three methods where appropriate. From the recoverable information, we deduce the existence of emergent $Z_2$ Gauss-law type constraints, which in turn imply emergent $Z_2$ conservation laws for point-like quasiparticle excitations of an underlying topologically ordered phase.

Categories: Journals, Physics
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