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QUROPE - aggregated feeds in category PhysicsenarXiv.org: Quantum Physics: Randomized Benchmarking, Correlated Noise, and Ising Models. (arXiv:1703.09747v1 [quant-ph])
http://arxiv.org/abs/1703.09747
<p>We compute the expected randomized benchmarking sequence fidelity for a
system subject to Gaussian time-correlated noise. For single qubit benchmarking
we show that the expected sequence fidelity is given by the partition function
of a long-range coupled spin-one Ising model, with each site in the Ising model
corresponding to a free evolution interval. For d-state systems, the expected
sequence fidelity is given by an Ising-like model partition function whose site
variables are given by the weights of the adjoint representation of SU(d).<p><a href="http://arxiv.org/abs/1703.09747">read more</a></p>
Thu, 30 Mar 2017 07:45:09 +0200arXiv.org: Quantum Physics: Error-transparent quantum gates for small logical qubit architectures. (arXiv:1703.09762v1 [quant-ph])
http://arxiv.org/abs/1703.09762
<p>One of the largest obstacles to building a quantum computer is gate error,
where the physical evolution of the state of a qubit or group of qubits during
a gate operation does not match the intended unitary transformation. Gate error
stems from a combination of control errors and random single qubit errors from
interaction with the environment. While great strides have been made in
mitigating control errors, intrinsic qubit error remains a serious problem that
sets the primary limit for gate fidelity in modern superconducting qubit
architectures.<p><a href="http://arxiv.org/abs/1703.09762">read more</a></p>
Thu, 30 Mar 2017 07:45:09 +0200arXiv.org: Quantum Physics: Light-matter quantum interferometry with homodyne detection. (arXiv:1703.09797v1 [quant-ph])
http://arxiv.org/abs/1703.09797
<p>We investigated the estimation of an unknown Gaussian process (containing
displacement, squeezing and phase-shift) applied to a matter system. The state
of the matter system is not directly measured, instead, we measure an optical
mode which interacts with the system. We propose an interferometric setup
exploiting a beam-splitter-type of light-matter interaction with homodyne
detectors and two methods of estimation.<p><a href="http://arxiv.org/abs/1703.09797">read more</a></p>
Thu, 30 Mar 2017 07:45:09 +0200arXiv.org: Quantum Physics: Dynamical engineering of interactions in qudit ensembles. (arXiv:1703.09808v1 [quant-ph])
http://arxiv.org/abs/1703.09808
<p>We propose and analyze a method to engineer effective interactions in an
ensemble of d-level systems (qudits) driven by global control fields. In
particular, we present (i) a necessary and sufficient condition under which a
given interaction can be turned off (decoupled), (ii) the existence of a
universal sequence that decouples any (cancellable) interaction, and (iii) an
efficient algorithm to engineer a target Hamiltonian from an initial
Hamiltonian (if possible).<p><a href="http://arxiv.org/abs/1703.09808">read more</a></p>
Thu, 30 Mar 2017 07:45:09 +0200arXiv.org: Quantum Physics: Chaos in de Broglie - Bohm quantum mechanics and the dynamics of quantum relaxation. (arXiv:1703.09810v1 [quant-ph])
http://arxiv.org/abs/1703.09810
<p>We discuss the main mechanisms generating chaotic behavior of the quantum
trajectories in the de Broglie - Bohm picture of quantum mechanics, in systems
of two and three degrees of freedom. In the 2D case, chaos is generated via
multiple scatterings of the trajectories with one or more `nodal point -
X-point complexes'. In the 3D case, these complexes form foliations along
`nodal lines' accompanied by `X-lines'. We also identify cases of integrable or
partially integrable quantum trajectories.<p><a href="http://arxiv.org/abs/1703.09810">read more</a></p>
Thu, 30 Mar 2017 07:45:09 +0200arXiv.org: Quantum Physics: Observation of Quantum Zeno blockade on Chip. (arXiv:1703.09830v1 [quant-ph])
http://arxiv.org/abs/1703.09830
<p>When overlapping in an optical medium with nonlinear susceptibility, light
waves can interact with each other, changing phases, wavelengths, shapes, and
so on. Such nonlinear effects, discovered over a half century ago, have given
rise to a breadth of applications. Applying to quantum-mechanical optical
signals, however, they face fundamental challenges arising from the multimode
nature of the interacting electromagnetic fields, such as phase noises and
Raman scattering.<p><a href="http://arxiv.org/abs/1703.09830">read more</a></p>
Thu, 30 Mar 2017 07:45:09 +0200arXiv.org: Quantum Physics: Randomized benchmarking with gate-dependent noise. (arXiv:1703.09835v1 [quant-ph])
http://arxiv.org/abs/1703.09835
<p>Previous analysis of randomized benchmarking assumed that experimental noise
"weakly" depends on the target gate. We show that this condition is more
restrictive than it initially appears, so much so that it is practically
unverifiable. We then resolve this limitation by proving that the exact impact
of gate-dependent noise can be described by a single perturbation term that
decays exponentially with the sequence length.<p><a href="http://arxiv.org/abs/1703.09835">read more</a></p>
Thu, 30 Mar 2017 07:45:09 +0200arXiv.org: Quantum Physics: On Monogamy of four qubit entanglement. (arXiv:1703.09861v1 [quant-ph])
http://arxiv.org/abs/1703.09861
<p>Our main result is a monogamy inequality satisfied by the entanglement of a
focus qubit (one-tangle) in a four-qubit pure state and entanglement of
subsystems. Analytical relations between three-tangles and two-tangles which
quantify the entanglement of marginal states and unitary invariants of
four-qubit pure state, are used to obtain the inequality. The contribution of
three-tangle to one-tangle is found to be half of that suggested by a simple
extension of entanglement monogamy relation for three qubits.<p><a href="http://arxiv.org/abs/1703.09861">read more</a></p>
Thu, 30 Mar 2017 07:45:09 +0200arXiv.org: Quantum Physics: A Direct Coupling Coherent Quantum Observer for a Qubit, including Observer Measurements. (arXiv:1703.09887v1 [quant-ph])
http://arxiv.org/abs/1703.09887
<p>This paper proposes a direct coupling coherent quantum observer for a quantum
plant which consists of a two level quantum system. The quantum observer, which
is a quantum harmonic oscillator, includes homodyne detection measurements. It
is shown that the observer can be designed so that it does not affect the
quantum variable of interest in the quantum plant and that measured output
converges in a given sense to the plant variable of interest. Also, the plant
variable of interest-observer system can be described by a set of linear
quantum stochastic differential equations.<p><a href="http://arxiv.org/abs/1703.09887">read more</a></p>
Thu, 30 Mar 2017 07:45:09 +0200arXiv.org: Quantum Physics: Optical Density-Enhanced Squeezed Light Generation without Optical Cavities. (arXiv:1703.09890v1 [quant-ph])
http://arxiv.org/abs/1703.09890
<p>To achieve high degree of quantum noise squeezing, an optical cavity is often
employed to enhance the interaction time between light and matter. Here, we
propose to utilize the effect of coherent population trapping (CPT) to directly
generate squeezed light without any optical cavity. Combined with the slow
propagation speed of light in a CPT medium, a coherent state passing through an
atomic ensemble with a high optical density (OD) can evolve into a highly
squeezed state even in a single passage.<p><a href="http://arxiv.org/abs/1703.09890">read more</a></p>
Thu, 30 Mar 2017 07:45:09 +0200