
Cosentino, A., & Russo, V. (2014). SMALL SETS OF LOCALLY INDISTINGUISHABLE ORTHOGONAL MAXIMALLY ENTANGLED STATES. Quantum Inform. Comput., 14(1314), 1098–1106.
Abstract: We study the problem of distinguishing quantum states using local operations and classical communication (LOCC). A question of fundamental interest is whether there exist sets of k <= d orthogonal maximally entangled states in Cd circle times Cd that are not perfectly distinguishable by LOCC. A recent result by Yu, Duan, and Ying [Phys. Rev. Lett. 109 020506 (2012)] gives an affirmative answer for the case k = d. We give, for the first time, a proof that such sets of states indeed exist even in the case k < d. Our result is constructive and holds for an even wider class of operations known as positivepartialtranspose measurements (PPT). The proof uses the characterization of the PPTdistinguishability problem as a semidefinite program.
Keywords: LOCC; PPT; state distinguishability; semidefinite programming


Grusdt, F., Abanin, D., & Demler, E. (2014). Measuring Z(2) topological invariants in optical lattices using interferometry. Phys. Rev. A, 89(4), 21 pp.
Abstract: We propose an interferometric method to measure Z(2) topological invariants of timereversal invariant topological insulators realized with optical lattices in two and three dimensions. We suggest two schemes which both rely on a combination of Bloch oscillations with Ramsey interferometry and can be implemented using standard tools of atomic physics. In contrast to topological Zak phase and Chern number, defined for individual onedimensional and twodimensional Bloch bands, the formulation of the Z(2) invariant involves at least two Bloch bands related by timereversal symmetry which one must keep track of in measurements. In one of our schemes this can be achieved by the measurement of Wilson loops, which are nonAbelian generalizations of Zak phases. The winding of their eigenvalues is related to the Z(2) invariant. We thereby demonstrate that Wilson loops are not just theoretical concepts but can be measured experimentally. For the second scheme we introduce a generalization of timereversal polarization which is continuous throughout the Brillouin zone. We show that its winding over half the Brillouin zone yields the Z(2) invariant. To measure this winding, our protocol only requires Bloch oscillations within a single band, supplemented by coherent transitions to a second band which can be realized by lattice shaking.


Marvian, I., & Spekkens, R. W. (2014). Asymmetry properties of pure quantum states. Phys. Rev. A, 90(1), 4 pp.
Abstract: The asymmetry properties of a state relative to some symmetry group specify how and to what extent the given symmetry is broken by the state. Characterizing these is found to be surprisingly useful for addressing a very common problem: to determine what follows from a system's dynamics (possibly open) having that symmetry. We demonstrate and exploit the fact that the asymmetry properties of a state can be understood in terms of informationtheoretic concepts. We show that for a pure state psi and a symmetry group G, they are completely specified by the characteristic function of the state, defined as chi(psi)(g) <psi broken vertical bar U (g) broken vertical bar psi >, where g is an element of G and U is the unitary representation of interest. Based on this observation, we study several important problems about the interconversion of pure states under symmetric dynamics, such as determining the conditions for reversible transformations, deterministic irreversible transformations, and asymptotic transformations.


Adamski, M. G., Gumann, P., & Baird, A. E. (2014). A Method for Quantitative Analysis of Standard and HighThroughput qPCR Expression Data Based on Input Sample Quantity. PLoS One, 9(8), 7 pp.
Abstract: Over the past decade rapid advances have occurred in the understanding of RNA expression and its regulation. Quantitative polymerase chain reactions (qPCR) have become the gold standard for quantifying gene expression. Microfluidic next generation, high throughput qPCR now permits the detection of transcript copy number in thousands of reactions simultaneously, dramatically increasing the sensitivity over standard qPCR. Here we present a gene expression analysis method applicable to both standard polymerase chain reactions (qPCR) and high throughput qPCR. This technique is adjusted to the input sample quantity (e. g., the number of cells) and is independent of control gene expression. It is efficiencycorrected and with the use of a universal reference sample (commercial complementary DNA (cDNA)) permits the normalization of results between different batches and between different instruments – regardless of potential differences in transcript amplification efficiency. Modifications of the input quantity method include (1) the achievement of absolute quantification and (2) a nonefficiency corrected analysis. When compared to other commonly used algorithms the input quantity method proved to be valid. This method is of particular value for clinical studies of whole blood and circulating leukocytes where cell counts are readily available.


Marvian, I., & Spekkens, R. W. (2014). A Generalization of SchurWeyl Duality with Applications in Quantum Estimation. Commun. Math. Phys., 331(2), 431–475.
Abstract: SchurWeyl duality is a powerful tool in representation theory which has many applications to quantum information theory. We provide a generalization of this duality and demonstrate some of its applications. In particular, we use it to develop a general framework for the study of a family of quantum estimation problems wherein one is given n copies of an unknown quantum state according to some prior and the goal is to estimate certain parameters of the given state. In particular, we are interested to know whether collective measurements are useful and if so to find an upper bound on the amount of entanglement which is required to achieve the optimal estimation. In the case of pure states, we show that commutativity of the set of observables that define the estimation problem implies the sufficiency of unentangled measurements.


Remko van den Hurk, N. N.  F. and S. E. (). Fabrication and characterization of aluminummolybdenum nanocomposite membranes. J. Vac. Sci. Technol. B, 32(5), 2002.
Abstract: Nanomembranes with thicknesses less than 100 nm and high widthtothickness ratios are of interest in sensing, energy storage, actuator, and optical applications. The fabrication of conductive nanocomposite aluminummolybdenum (AlMo) membranes as thin as 28 nm and high fracture strength is reported. The density, Poisson's ratio, and Young's modulus of the membranes were determined to be ρ = 5000 ± 550 kg/m3, σ = 0.33 ± 0.05, and E = 127 ± 21 GPa, respectively. The intrinsic stress of the membranes was determined by bulge testing, finite element analysis (FEA), and classical mechanics. The resonance frequencies of the membranes were assessed using FEA and measured by optical interferometry. The fracture strength of the AlMo membranes was 1.89 ± 0.45 GPa, and the average resistivity was ρ = 5810 ± 44 μΩ cm. The high fracture strength and low resistivity of such AlMo membranes makes them attractive in the design of microdevices requiring ultrathin yet electrically conductive membranes.


Grusdt, F., Abanin, D., & Demler, E. (2014). Measuring Z(2) topological invariants in optical lattices using interferometry. Phys. Rev. A, 89(4), 21 pp.
Abstract: We propose an interferometric method to measure Z(2) topological invariants of timereversal invariant topological insulators realized with optical lattices in two and three dimensions. We suggest two schemes which both rely on a combination of Bloch oscillations with Ramsey interferometry and can be implemented using standard tools of atomic physics. In contrast to topological Zak phase and Chern number, defined for individual onedimensional and twodimensional Bloch bands, the formulation of the Z(2) invariant involves at least two Bloch bands related by timereversal symmetry which one must keep track of in measurements. In one of our schemes this can be achieved by the measurement of Wilson loops, which are nonAbelian generalizations of Zak phases. The winding of their eigenvalues is related to the Z(2) invariant. We thereby demonstrate that Wilson loops are not just theoretical concepts but can be measured experimentally. For the second scheme we introduce a generalization of timereversal polarization which is continuous throughout the Brillouin zone. We show that its winding over half the Brillouin zone yields the Z(2) invariant. To measure this winding, our protocol only requires Bloch oscillations within a single band, supplemented by coherent transitions to a second band which can be realized by lattice shaking.


Grusdt, F., Abanin, D., & Demler, E. (2014). Measuring Z(2) topological invariants in optical lattices using interferometry. Phys. Rev. A, 89(4), 21 pp.
Abstract: We propose an interferometric method to measure Z(2) topological invariants of timereversal invariant topological insulators realized with optical lattices in two and three dimensions. We suggest two schemes which both rely on a combination of Bloch oscillations with Ramsey interferometry and can be implemented using standard tools of atomic physics. In contrast to topological Zak phase and Chern number, defined for individual onedimensional and twodimensional Bloch bands, the formulation of the Z(2) invariant involves at least two Bloch bands related by timereversal symmetry which one must keep track of in measurements. In one of our schemes this can be achieved by the measurement of Wilson loops, which are nonAbelian generalizations of Zak phases. The winding of their eigenvalues is related to the Z(2) invariant. We thereby demonstrate that Wilson loops are not just theoretical concepts but can be measured experimentally. For the second scheme we introduce a generalization of timereversal polarization which is continuous throughout the Brillouin zone. We show that its winding over half the Brillouin zone yields the Z(2) invariant. To measure this winding, our protocol only requires Bloch oscillations within a single band, supplemented by coherent transitions to a second band which can be realized by lattice shaking.


Shashi, A., Grusdt, F., Abanin, D. A., & Demler, E. (2014). Radiofrequency spectroscopy of polarons in ultracold Bose gases. Phys. Rev. A, 89(5), 17 pp.
Abstract: Recent experimental advances enabled the realization of mobile impurities immersed in a BoseEinstein condensate (BEC) of ultracold atoms. Here, we consider impurities with two or more internal hyperfine states, and study their radiofrequency (rf) absorption spectra, which correspond to transitions between two different hyperfine states. We calculate rf spectra for the case when one of the hyperfine states involved interacts with the BEC, while the other state is noninteracting, by performing a nonperturbative resummation of the probabilities of exciting different numbers of phonon modes. In the presence of interactions, the impurity gets dressed by Bogoliubov excitations of the BEC, and forms a polaron. The rf signal contains a deltafunction peak centered at the energy of the polaron measured relative to the bare impurity transition frequency with a weight equal to the amount of bare impurity character in the polaron state. The rf spectrum also has a broad incoherent part arising from the background excitations of the BEC, with a characteristic powerlaw tail that appears as a consequence of the universal physics of contact interactions. We discuss both the direct rf measurement, in which the impurity is initially in an interacting state, and the inverse rf measurement, in which the impurity is initially in a noninteracting state. In the latter case, in order to calculate the rf spectrum, we solve the problem of polaron formation: a mobile impurity is suddenly introduced in a BEC, and dynamically gets dressed by Bogoliubov phonons. Our solution is based on a timedependent variational ansatz of coherent states of Bogoliubov phonons, which becomes exact when the impurity is localized. Moreover, we show that such an ansatz compares well with a semiclassical estimate of the propagation amplitude of a mobile impurity in the BEC. Our technique can be extended to cases when both initial and final impurity states are interacting with the BEC.


Fritsch, K., Kermarrec, E., Ross, K. A., Qiu, Y., Copley, J. R. D., Pomaranski, D., et al. (2014). Temperature and magnetic field dependence of spinice correlations in the pyrochlore magnet Tb2Ti2O7. Phys. Rev. B, 90(1), 9 pp.
Abstract: We present a parametric study of the diffuse magnetic scattering at (1/2, 1/2, 1/2) positions in reciprocal space, ascribed to a frozen antiferromagnetic spin ice state in singlecrystalline Tb2Ti2O7. Our highresolution neutron scattering measurements show that the elastic (0.02 meV < E < 0.02 meV) (1/2, 1/2, 1/2) scattering develops strongly below approximate to 275 mK, and correlates with the opening of a spin gap of approximate to 0.06 to 0.08 meV over most of the Brillouin zone. The nature of the transition at 275 mK has many characteristics of spin glass behavior, consistent with acsusceptibility measurements. The application of a magnetic field of 0.075 T applied along the [1 (1) over bar0] direction destroys the (1/2, 1/2, 1/2) elastic scattering, revealing the fragility of this shortrange ordered ground state. We construct a refined HT phase diagram for Tb2Ti2O7 and [1 (1) over bar0] fields which incorporates this frozen spin ice regime and the antiferromagnetic longrange order previously known to be induced in relatively large fields. Specific heat measurements on the same crystal reveal a sharp anomaly at Tc approximate to 450 mK and no indication of a transition near approximate to 275 mK. We conclude that the higher temperature specific heat peak is not related to the magnetic ordering but is likely a signal of other, nonmagnetic dipole correlations.


Agnew, M., Bolduc, E., Resch, K. J., FrankeArnold, S., & Leach, J. (2014). Discriminating SinglePhoton States Unambiguously in High Dimensions. Phys. Rev. Lett., 113(2), 5 pp.
Abstract: The ability to uniquely identify a quantum state is integral to quantum science, but for nonorthogonal states, quantum mechanics precludes deterministic, errorfree discrimination. However, using the nondeterministic protocol of unambiguous state discrimination enables the errorfree differentiation of states, at the cost of a lower frequency of success. We discriminate experimentally between nonorthogonal, highdimensional states encoded in single photons; our results range from dimension d = 2 to d = 14. We quantify the performance of our method by comparing the total measured error rate to the theoretical rate predicted by minimumerror state discrimination. For the chosen states, we find a lower error rate by more than 1 standard deviation for dimensions up to d = 12. This method will find immediate application in highdimensional implementations of quantum information protocols, such as quantum cryptography.


Wang, J., Byrd, J. N., Simbotin, I., & Cote, R. (2014). Tuning Ultracold Chemical Reactions via RydbergDressed Interactions. Phys. Rev. Lett., 113(2), 5 pp.
Abstract: We show that ultracold chemical reactions with an activation barrier can be tuned using Rydbergdressed interactions. Scattering in the ultracold regime is sensitive to longrange interactions, especially when weakly bound (or quasibound) states exist near the collision threshold. We investigate how, by Rydberg dressing a reactant, one enhances its polarizability and modifies the longrange van der Waals collision complex, which can alter chemical reaction rates by shifting the position of nearthreshold bound states. We carry out a full quantum mechanical scattering calculation for the benchmark system H2 + D, and show that resonances can be moved substantially and that rate coefficients at cold and ultracold temperatures can be increased by several orders of magnitude.


Repellin, C., Neupert, T., Papic, Z., & Regnault, N. (2014). Singlemode approximation for fractional Chern insulators and the fractional quantum Hall effect on the torus. Phys. Rev. B, 90(4), 11 pp.
Abstract: We analyze the collective magnetoroton excitations of bosonic Laughlin v = 1/2 fractional quantum Hall (FQH) states on the torus and of their analog on the lattice, the fractional Chern insulators (FCIs). We show that, by applying the appropriate mapping of momentum quantum numbers between the two systems, the magnetoroton mode can be identified in FCIs and that it contains the same number of states as in the FQH case. Further, we numerically test the singlemode approximation to the magnetoroton mode for both the FQH and FCI cases. This proves particularly challenging for the FCI because its eigenstates have a lower translational symmetry than the FQH states. In spite of this, we construct the FCI singlemode approximation such that it carries the same momenta as the FQH states, allowing for a direct comparison between the two systems. We show that the singlemode approximation captures well a dispersive subset of the magnetoroton excitations both for the FQH and the FCI cases. We find remarkable quantitative agreement between the two systems. For example, the manybody excitation gap extrapolates to almost the same value in the thermodynamic limit.


Leung, D., Li, K., Smith, G., & Smolin, J. A. (2014). Maximal Privacy without Coherence. Phys. Rev. Lett., 113(3), 5 pp.
Abstract: Privacy is a fundamental feature of quantum mechanics. A coherently transmitted quantum state is inherently private. Remarkably, coherent quantum communication is not a prerequisite for privacy: there are quantum channels that are too noisy to transmit any quantum information reliably that can nevertheless send private classical information. Here, we ask how much private classical information a channel can transmit if it has little quantum capacity. We present a class of channels Nd with input dimension d(2), quantum capacity Q(Nd) <= 1, and private capacity P(Nd) = log d. These channels asymptotically saturate an interesting inequality P(N) <= (1/2) [log d(A) + Q(N)] for any channel N with input dimension d(A) and capture the essence of privacy stripped of the confounding influence of coherence.


Ito, T. (2014). Parallelization of entanglementresistant multiprover interactive proofs. Inf. Process. Lett., 114(10), 579–583.
Abstract: Multiprover interactive proof systems are said to be entanglementresistant if the soundness holds even when provers are allowed to share an arbitrary quantum state before the interaction starts. This letter proves that every entanglementresistant multiprover interactive proof system can be parallelized to two rounds without ruining its entanglement resistance at the expense of adding one prover. (C) 2014 Elsevier B.V. All rights reserved.
Keywords: Computational complexity; Quantum computing; Interactive proof; Quantum nonlocality


