In this Letter, we propose a framework to transform a complex network to a time series. The transformation from complex networks to time series is realized by the classical multidimensional scaling. Applying the transformation method to a model proposed by Watts and Strogatz [Nature (London) 393, 440 (1998)], we show that ring lattices are transformed to periodic time series, small-world networks to noisy periodic time series, and random networks to random time series. We also show that these relationships are analytically held by using the circulant-matrix theory and the perturbation theory of linear operators. The results are generalized to several high-dimensional lattices.

We derive a tight bound between the quality of estimating a quantum state by measurement and the success probability of undoing the measurement in arbitrary dimensional systems, which completely describes the tradeoff relation between the information gain and reversibility. In this formulation, it is clearly shown that the information extracted from a weak measurement is erased through the reversing process. Our result broadens the information-theoretic perspective on quantum measurement as well as provides a standard tool to characterize weak measurements and reversals.

The dynamics of the environment is usually experimentally inaccessible and hence ignored for open systems. Here we overcome this limitation by using an interferometric setup that allows the implementation of several decoherence channels and full access to all environmental degrees of freedom. We show that when a qubit from an entangled pair interacts with the environment, the initial bipartite entanglement gets redistributed into bipartite and genuine multipartite entanglements involving the two qubits and the environment. This is yet another trait of the subtle behavior of entangled open systems.

Perhaps the quantum state represents information about reality, and not reality directly. Wave function collapse is then possibly no more mysterious than a Bayesian update of a probability distribution given new data. We consider models for quantum systems with measurement outcomes determined by an underlying physical state of the system but where several quantum states are consistent with a single underlying state—i.e., probability distributions for distinct quantum states overlap. Significantly, we demonstrate by example that additional assumptions are always necessary to rule out such a model.

We discuss fluctuations near the second-order phase transition where the free energy has an additional non-Hermitian term. The spectrum of the fluctuations changes when the odd-parity potential amplitude exceeds the critical value corresponding to the $\mathcal{P}\mathcal{T}$-symmetry breakdown in the topological structure of the Hilbert space of the effective non-Hermitian Hamiltonian. We calculate the fluctuation contribution to the differential resistance of a superconducting weak link and find the manifestation of the $\mathcal{P}\mathcal{T}$-symmetry breaking in its temperature evolution. We successfully validate our theory by carrying out measurements of far from equilibrium transport in mesoscale-patterned superconducting wires.

We study rainbow (fold) and cusp catastrophes that form in Fock space following a quench in a Bose Josephson junction. In the Gross-Pitaevskii mean-field theory, the rainbows are singular caustics, but in the second-quantized theory a Poisson resummation of the wave function shows that they are described by well-behaved Airy functions. The structural stability of these Fock space caustics against variations in the initial conditions and Hamiltonian evolution is guaranteed by catastrophe theory. We also show that the long-time dynamics are ergodic. Our results are relevant to the question posed by Berry [M. V. Berry, Nonlinearity 21, T19 (2008)]: Are there circumstances when it is necessary to second quantize wave theory in order to avoid singularities?

In the setting of networked computation, data security can be a significant concern. Here we consider the problem of allowing a server to remotely manipulate client supplied data, in such a way that both the information obtained by the client about the server’s operation and the information obtained by the server about the client’s data are significantly limited. We present a protocol for achieving such functionality in two closely related models of restricted quantum computation—the boson sampling and quantum walk models. Because of the limited technological requirements of the boson scattering model, small scale implementations of this technique are feasible with present-day technology.

We provide the first evidence for a holographic correspondence between a gravitational theory in flat space and a specific unitary field theory in one dimension lower. The gravitational theory is a flat-space limit of topologically massive gravity in three dimensions at a Chern–Simons level of $k=1$. The field theory is a chiral two-dimensional conformal field theory with a central charge of $c=24$.

The Polyakov loop has been used repeatedly as an order parameter in the deconfinement phase transition in QCD. We argue that, in the confined phase, its expectation value can be represented in terms of hadronic states, similarly to the hadron resonance gas model for the pressure. Specifically, $L(T)\approx \frac{1}{2}\sum _{\alpha }{g}_{\alpha }{e}^{-{\Delta }_{\alpha }/T}$, where $g_{\alpha }$ are the degeneracies and ${\Delta }_{\alpha }$ are the masses of hadrons with exactly one heavy quark (the mass of the heavy quark itself being subtracted). We show that this approximate sum rule gives a fair description of available lattice data with $N_f=2+1$ for temperatures in the range $150\mathrm{MeV}<T<190\mathrm{MeV}$ with conventional meson and baryon states from two different models. For temperatures below 150 MeV different lattice results disagree. One set of data can be described if exotic hadrons are present in the QCD spectrum while other sets do not require such states.

The dependence of the confinement transition parameters on the fermion content provides information on the mechanism of confinement. Recent progress in lattice gauge theories has allowed us to study it for a light flavor number $N_f\sim O(10)$ and found this transition to shift toward significantly stronger coupling. We propose an explanation for that: light fermions can occupy the chromomagnetic monopoles, via zero modes, making them “distinguishable” and unsuitable for Bose-Einstein condensation. Such dilution of unoccupied monopoles is compensated by stronger coupling that makes them lighter and more numerous. We also suggest that flavor-carrying quark-monopole objects account for the density beyond the quark Fermi sphere seen in the cold dense phase of $N_c=2$ lattice QCD.

The effective lifetime of the ${\overline{B}}_s^0$ meson in the decay mode ${\overline{B}}_s^0\to J/\psi f_0(980)$ is measured using $1.0{\mathrm{fb}}^{-1}$ of data collected in $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ with the LHCb detector. The result is $1.700\pm 0.040\pm 0.026\mathrm{ps}$, where the first uncertainty is statistical and the second systematic. As the final state is $CP$-odd, and $CP$ violation in this mode is measured to be small, the lifetime measurement can be translated into a measurement of the decay width of the heavy ${\overline{B}}_s^0$ mass eigenstate, ${\Gamma }_H=0.588\pm 0.014\pm 0.009{\mathrm{ps}}^{-1}$.

We present a precision measurement of the top-quark mass using the full sample of Tevatron $\sqrt{s}=1.96\mathrm{TeV}$ proton-antiproton collisions collected by the CDF II detector, corresponding to an integrated luminosity of $8.7{\mathrm{fb}}^{-1}$. Using a sample of $t\overline{t}$ candidate events decaying into the $\mathrm{\text{lepton}}+\mathrm{\text{jets}}$ channel, we obtain distributions of the top-quark masses and the invariant mass of two jets from the $W$ boson decays from data. We then compare these distributions to templates derived from signal and background samples to extract the top-quark mass and the energy scale of the calorimeter jets with in situ calibration. The likelihood fit of the templates from signal and background events to the data yields the single most-precise measurement of the top-quark mass, $M_{\mathrm{top}}=172.85\pm 0.71(\mathrm{stat})\pm 0.85(\mathrm{syst})\mathrm{GeV}/c^2$.

The polarization of a top quark can be sensitive to new physics beyond the standard model. Since the charged lepton from top-quark decay is maximally correlated with the top-quark spin, it is common to measure the polarization from the distribution in the angle between the charged lepton and the top-quark directions. We propose a novel method based on the charged lepton energy fraction and illustrate the method with a detailed simulation of top-quark pairs produced in supersymmetric top squark pair production. We show that the lepton energy ratio distribution that we define is very sensitive to the top-quark polarization but insensitive to the precise measurement of the top-quark energy.

Neutral-pion ${\pi }^0$ spectra were measured at midrapidity ($|y|<0.35$) in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=39$ and 62.4 GeV and compared with earlier measurements at 200 GeV in a transverse-momentum range of $1<p_T<10\mathrm{GeV}/c$. The high-$p_T$ tail is well described by a power law in all cases, and the powers decrease significantly with decreasing center-of-mass energy. The change of powers is very similar to that observed in the corresponding spectra for $p+p$ collisions. The nuclear modification factors ($R_{AA}$) show significant suppression, with a distinct energy, centrality, and $p_T$ dependence. Above $p_T=7\mathrm{GeV}/c$, $R_{AA}$ is similar for $\sqrt{s_{\mathrm{NN}}}=62.4$ and 200 GeV at all centralities. Perturbative-quantum-chromodynamics calculations that describe $R_{AA}$ well at 200 GeV fail to describe the 39 GeV data, raising the possibility that, for the same $p_T$ region, the relative importance of initial-state effects and soft processes increases at lower energies. The $p_T$ range where ${\pi }^0$ spectra in central $\mathrm{Au}+\mathrm{Au}$ collisions have the same power as in $p+p$ collisions is $\approx 5$ and $7\mathrm{GeV}/c$ for $\sqrt{s_{\mathrm{NN}}}=200$ and 62.4 GeV, respectively. For the $\sqrt{s_{\mathrm{NN}}}=39\mathrm{GeV}$ data, it is not clear whether such a region is reached, and the $x_T$ dependence of the $x_T$-scaling power-law exponent is very different from that observed in the $\sqrt{s_{\mathrm{NN}}}=62$ and 200 GeV data, providing further evidence that initial-state effects and soft processes mask the in-medium suppression of hard-scattered partons to higher $p_T$ as the collision energy decreases.

We report the measurement of direct photons at midrapidity in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. The direct photon signal was extracted for the transverse momentum range of $4\mathrm{GeV}/c<p_T<22\mathrm{GeV}/c$, using a statistical method to subtract decay photons from the inclusive photon sample. The direct photon nuclear modification factor $R_{\mathrm{AA}}$ was calculated as a function of $p_T$ for different $\mathrm{Au}+\mathrm{Au}$ collision centralities using the measured $p+p$ direct photon spectrum and compared to theoretical predictions. $R_{\mathrm{AA}}$ was found to be consistent with unity for all centralities over the entire measured $p_T$ range. Theoretical models that account for modifications of initial direct photon production due to modified parton distribution functions in Au and the different isospin composition of the nuclei predict a modest change of $R_{\mathrm{AA}}$ from unity. They are consistent with the data. Models with compensating effects of the quark-gluon plasma on high-energy photons, such as suppression of jet-fragmentation photons and induced-photon bremsstrahlung from partons traversing the medium, are also consistent with this measurement.

We observe measurement-induced qubit state mixing in a transmon qubit dispersively coupled to a planar readout cavity. Our results indicate that dephasing noise at the qubit-readout detuning frequency is up-converted by readout photons to cause spurious qubit state transitions, thus limiting the nondemolition character of the readout. Furthermore, we use the qubit transition rate as a tool to extract an equivalent flux noise spectral density at $f\sim 1\mathrm{GHz}$ and find agreement with values extrapolated from a $1/f^{\alpha }$ fit to the measured flux noise spectral density below 1 Hz.

We investigate a nonlinear coherent feedback circuit constructed from preexisting superconducting microwave devices. The network exhibits emergent bistable and astable states, and we demonstrate its operation as a latch and the frequency locking of its oscillations. While the network is tedious to model by hand, our observations agree quite well with the semiclassical dynamical model produced by a new software package (N. Tezak et al., arXiv:1111.3081v1 [Phil. Trans. R. Soc. A (to be published)]) that systematically interpreted an idealized schematic of the system as a quantum optic feedback network.

Wave transport in a media with a slow spatial gradient of its characteristics is found to exhibit a universal wave pattern (“gradient marker”) in a vicinity of the maxima or minima of the gradient. The pattern is common for optics, quantum mechanics, and any other propagation governed by the same wave equation. Derived analytically, it has an elegantly simple yet nontrivial profile found in perfect agreement with numerical simulations for specific examples. We also find resonant states in continuum in the case of quantum wells, and formulated criteria for their existence.

We prove an analytical limitation on the use of time-delayed feedback control for the stabilization of periodic orbits in autonomous systems. This limitation depends on the number of real Floquet multipliers larger than unity, and is therefore similar to the well-known odd number limitation of time-delayed feedback control. Recently, a two-dimensional example has been found, which explicitly demonstrates that the unmodified odd number limitation does not apply in the case of autonomous systems. We show that our limitation correctly predicts the stability boundaries in this case.

The heat transfer efficiency in turbulent Rayleigh-Bénard convection is investigated experimentally, in a cylindrical cell of height 0.3 m, diameter 0.3 m. We show that for Rayleigh numbers ${10}^{12}\lesssim \mathrm{Ra}\lesssim {10}^{15}$ the Nusselt number closely follows $\mathrm{Nu}\propto {\mathrm{Ra}}^{1/3}$ if the mean temperature of the working fluid—cryogenic helium gas—is measured by small sensors directly inside the cell at about half of its height. In contrast, if the mean temperature is determined in a conventional way, as an arithmetic mean of the bottom and top plate temperatures, the $\mathrm{Nu}(\mathrm{Ra})\propto {\mathrm{Ra}}^{\gamma }$ displays spurious crossover to higher $\gamma$ that might be misinterpreted as a transition to the ultimate Kraichnan regime.