Statistical Mechanical Approach to the Equation of State of Unitary Fermi Gases
De Silva, Theja N
2016-01-01
We combine a Tan's universal relation with a basic statistical mechanical approach to derive a general equation of state for unitary Fermi gases. The universal equation of state is written as a series solution to a self consistent integral equation where the general solution is a linear combination of Fermi functions. By truncating our series solution to four terms with already known exact theoretical inputs at limiting cases, namely the first three virial coefficients and the Bertsch parameter, we find a good agreement with experimental measurements in the entire temperature region in the normal state. Our analytical equation of state agrees with experimental data up to the fugacity $z = 18$, which is a vast improvement over the other analytical equations of state available where the agreements is \\emph{only} up to $z \\approx 7$.
A Proposal for measuring Anisotropic Shear Viscosity in Unitary Fermi Gases
Samanta, Rickmoy; Trivedi, Sandip P
2016-01-01
We present a proposal to measure anisotropic shear viscosity in a strongly interacting, ultra-cold, unitary Fermi gas confined in a harmonic trap. We introduce anisotropy in this setup by strongly confining the gas in one of the directions with relatively weak confinement in the remaining directions. This system has a close resemblance to anisotropic strongly coupled field theories studied recently in the context of gauge-gravity duality. Computations in such theories (which have gravity duals) revealed that some of the viscosity components of the anisotropic shear viscosity tensor can be made much smaller than the entropy density, thus parametrically violating the bound proposed by Kovtun, Son and Starinets (KSS): $\\frac {\\eta} {s} \\geq \\frac{1}{4 \\pi}$. A Boltzmann analysis performed in a system of weakly interacting particles in a linear potential also shows that components of the viscosity tensor can be reduced. Motivated by these exciting results, we propose two hydrodynamic modes in the unitary Fermi ga...
Virial theorem and universality in a unitary fermi gas.
Thomas, J E; Kinast, J; Turlapov, A
2005-09-16
Unitary Fermi gases, where the scattering length is large compared to the interparticle spacing, can have universal properties, which are independent of the details of the interparticle interactions when the range of the scattering potential is negligible. We prepare an optically trapped, unitary Fermi gas of 6Li, tuned just above the center of a broad Feshbach resonance. In agreement with the universal hypothesis, we observe that this strongly interacting many-body system obeys the virial theorem for an ideal gas over a wide range of temperatures. Based on this result, we suggest a simple volume thermometry method for unitary gases. We also show that the observed breathing mode frequency, which is close to the unitary hydrodynamic value over a wide range of temperature, is consistent with a universal hydrodynamic gas with nearly isentropic dynamics.
The universal sound velocity formula for the strongly interacting unitary Fermi gas
Institute of Scientific and Technical Information of China (English)
Liu Ke; Chen Ji-Sheng
2011-01-01
Due to the scale invariance, the thermodynamic laws of strongly interacting limit unitary Fermi gas can be similar to those of non-interacting ideal gas. For example, the virial theorem between pressure and energy density of the ideal gas P = 2E/ZV is still satisfied by the unitary Fermi gas. This paper analyses the sound velocity of unitary Fermi gases with the quasi-linear approximation. For comparison, the sound velocities for the ideal Boltzmann, Bose and Fermi gas are also given. Quite interestingly, the sound velocity formula for the ideal non-interacting gas is found to be satisfied by the unitary Fermi gas in different temperature regions.
Strongly interacting Fermi gases
Directory of Open Access Journals (Sweden)
Bakr W.
2013-08-01
Full Text Available Strongly interacting gases of ultracold fermions have become an amazingly rich test-bed for many-body theories of fermionic matter. Here we present our recent experiments on these systems. Firstly, we discuss high-precision measurements on the thermodynamics of a strongly interacting Fermi gas across the superfluid transition. The onset of superfluidity is directly observed in the compressibility, the chemical potential, the entropy, and the heat capacity. Our measurements provide benchmarks for current many-body theories on strongly interacting fermions. Secondly, we have studied the evolution of fermion pairing from three to two dimensions in these gases, relating to the physics of layered superconductors. In the presence of p-wave interactions, Fermi gases are predicted to display toplogical superfluidity carrying Majorana edge states. Two possible avenues in this direction are discussed, our creation and direct observation of spin-orbit coupling in Fermi gases and the creation of fermionic molecules of 23Na 40K that will feature strong dipolar interactions in their absolute ground state.
Shear Viscosity of a Unitary Fermi Gas
Wlazłowski, Gabriel; Magierski, Piotr; Drut, Joaquín E.
2012-01-01
We present the first ab initio determination of the shear viscosity eta of the Unitary Fermi Gas, based on finite temperature quantum Monte Carlo calculations and the Kubo linear-response formalism. We determine the temperature dependence of the shear viscosity to entropy density ratio eta/s. The minimum of eta/s appears to be located above the critical temperature for the superfluid-to-normal phase transition with the most probable value being eta/s approx 0.2 hbar/kB, which almost saturates...
Shortcut to adiabaticity for an anisotropic unitary Fermi gas
Deng, Shujin; Yu, Qianli; Wu, Haibin
2016-01-01
Coherent control of complex quantum systems is a fundamental requirement in quantum information processing and engineering. Recently developed notion of shortcut to adiabaticity (STA) has spawned intriguing prospects. So far, the most experimental investigations of STA are implemented in the ideal thermal gas or the weakly interacting ultracold Bose gases. Here we report the first demonstration of a many-body STA in a 3D anisotropically trapped unitary Fermi gas. A new dynamical scaling law is demonstrated on such a strongly interacting quantum gas. By simply engineering the frequency aspect ratio of a harmonic trap, the dynamics of the gas can be manipulated and the many-body state can be transferred adiabatically from one stationary state to another one in short time scale without the excitation. The universal scaling both for non-interacting and unitary Fermi gas is also verified. This could be very important for future many-body quantum engineering and the exploration of the fundamental law of the thermod...
Imbalanced Fermi gases at unitarity
Gubbels, K.B.; Stoof, H.T.C.
2013-01-01
We consider imbalanced Fermi gases with strong attractive interactions, for which Cooper-pair formation plays an important role. The two-component mixtures consist either of identical fermionic atoms in two different hyperfine states, or of two different atomic species both occupying only a single
Temperature dependence of the universal contact parameter in a unitary Fermi gas.
Kuhnle, E D; Hoinka, S; Dyke, P; Hu, H; Hannaford, P; Vale, C J
2011-04-29
The contact I, introduced by Tan, has emerged as a key parameter characterizing universal properties of strongly interacting Fermi gases. For ultracold Fermi gases near a Feshbach resonance, the contact depends upon two quantities: the interaction parameter 1/(k(F)a), where k(F) is the Fermi wave vector and a is the s-wave scattering length, and the temperature T/T(F), where T(F) is the Fermi temperature. We present the first measurements of the temperature dependence of the contact in a unitary Fermi gas using Bragg spectroscopy. The contact is seen to follow the predicted decay with temperature and shows how pair-correlations at high momentum persist well above the superfluid transition temperature.
The Shear Viscosity in an Anisotropic Unitary Fermi Gas
Samanta, Rickmoy; Trivedi, Sandip P
2016-01-01
We consider a system consisting of a strongly interacting, ultracold unitary Fermi gas under harmonic confinement. Our analysis suggests the possibility of experimentally studying, in this system, an anisotropic shear viscosity tensor driven by the anisotropy in the trapping potential. In particular, we suggest that this experimental setup could mimic some features of anisotropic geometries that have recently been studied for strongly coupled field theories which have a gravitational dual. Results using the AdS/CFT correspondence in these theories show that in systems with a background linear potential, certain viscosity components can be made much smaller than the entropy density, parametrically violating the KSS bound. This intuition, along with results from a Boltzmann analysis that we perform, suggests that a violation of the KSS bound can perhaps occur in the unitary Fermi gas system when it is subjected to a suitable anisotropic trapping potential. We give a concrete proposal for an experimental setup w...
Strongly Interacting Fermi Gases in Two Dimensions
2012-07-17
Svistunov, M. Ku, A. Sommer, L. W. Cheuk, A. Schirotzek, M. W. Zwierlein Feynman diagrams versus Fermi-gas Feynman emulator Nature Physics 8... Feynman emulator. Nature Physics 8, 366 (2012) 4. Jee Woo Park, Cheng-Hsun Wu, Ibon Santiago, Tobias G. Tiecke, Peyman Ahmadi, Martin W. Zwierlein...chapters 7. M. Randeria, W. Zwerger, and M. Zwierlein. The BEC-BCS Crossover and the Unitary Fermi Gas. Lecture Notes in Physics , Volume 836, edited by
Quantized superfluid vortex rings in the unitary Fermi gas.
Bulgac, Aurel; Forbes, Michael McNeil; Kelley, Michelle M; Roche, Kenneth J; Wlazłowski, Gabriel
2014-01-17
In a recent article, Yefsah et al. [Nature (London) 499, 426 (2013)] report the observation of an unusual excitation in an elongated harmonically trapped unitary Fermi gas. After phase imprinting a domain wall, they observe oscillations almost an order of magnitude slower than predicted by any theory of domain walls which they interpret as a "heavy soliton" of inertial mass some 200 times larger than the free fermion mass or 50 times larger than expected for a domain wall. We present compelling evidence that this "soliton" is instead a quantized vortex ring, by showing that the main aspects of the experiment can be naturally explained within the framework of time-dependent superfluid density functional theories.
DEFF Research Database (Denmark)
Bruun, Georg
2011-01-01
We examine spin diffusion in a two-component homogeneous Fermi gas in the normal phase. Using a variational approach, analytical results are presented for the spin diffusion coefficient and the related spin relaxation time as a function of temperature and interaction strength. For low temperatures......, strong correlation effects are included through the Landau parameters which we extract from Monte Carlo results. We show that the spin diffusion coefficient has a minimum for a temperature somewhat below the Fermi temperature with a value that approaches the quantum limit ~/m in the unitarity regime...
Dark lump excitations in superfluid Fermi gases
Institute of Scientific and Technical Information of China (English)
Xu Yan-Xia; Duan Wen-Shan
2012-01-01
We study the linear and nonlinear properties of two-dimensional matter-wave pulses in disk-shaped superfluid Fermi gases.A Kadomtsev Petviashvili I (KPI) solitary wave has been realized for superfluid Fermi gases in the limited cases of Bardeen-Cooper-Schrieffer (BCS) regime,Bose-Einstein condensate (BEC) regime,and unitarity regime.Onelump solution as well as one-line soliton solutions for the KPI equation are obtained,and two-line soliton solutions with the same amplitude are also studied in the limited cases.The dependence of the lump propagating velocity and the sound speed of two-dimensional superfluid Fermi gases on the interaction parameter are investigated for the limited cases of BEC and unitarity.
Itinerant Ferromagnetism in Ultracold Fermi Gases
DEFF Research Database (Denmark)
Heiselberg, Henning
2012-01-01
Itinerant ferromagnetism in cold Fermi gases with repulsive interactions is studied applying the Jastrow-Slater approximation generalized to finite polarization and temperature. For two components at zero temperature a second order transition is found at akF ≃ 0.90 compatible with QMC. Thermodyna......Itinerant ferromagnetism in cold Fermi gases with repulsive interactions is studied applying the Jastrow-Slater approximation generalized to finite polarization and temperature. For two components at zero temperature a second order transition is found at akF ≃ 0.90 compatible with QMC...
Bragg spectroscopy of strongly interacting Fermi gases
Lingham, M. G.; Fenech, K.; Peppler, T.; Hoinka, S.; Dyke, P.; Hannaford, P.; Vale, C. J.
2016-10-01
This article provides an overview of recent developments and emerging topics in the study of two-component Fermi gases using Bragg spectroscopy. Bragg scattering is achieved by exposing a gas to two intersecting laser beams with a slight frequency difference and measuring the momentum transferred to the atoms. By varying the Bragg laser detuning, it is possible to measure either the density or spin response functions which characterize the basic excitations present in the gas. Specifically, one can measure properties such as the dynamic and static structure factors, Tan's universal contact parameter and observe signatures for the onset of pair condensation locally within a gas.
Detecting Friedel oscillations in ultracold Fermi gases
Riechers, Keno; Hueck, Klaus; Luick, Niclas; Lompe, Thomas; Moritz, Henning
2017-09-01
Investigating Friedel oscillations in ultracold gases would complement the studies performed on solid state samples with scanning-tunneling microscopes. In atomic quantum gases interactions and external potentials can be tuned freely and the inherently slower dynamics allow to access non-equilibrium dynamics following a potential or interaction quench. Here, we examine how Friedel oscillations can be observed in current ultracold gas experiments under realistic conditions. To this aim we numerically calculate the amplitude of the Friedel oscillations which are induced by a potential barrier in a 1D Fermi gas and compare it to the expected atomic and photonic shot noise in a density measurement. We find that to detect Friedel oscillations the signal from several thousand one-dimensional systems has to be averaged. However, as up to 100 parallel one-dimensional systems can be prepared in a single run with present experiments, averaging over about 100 images is sufficient.
Dimensional BCS-BEC crossover in ultracold Fermi gases
Energy Technology Data Exchange (ETDEWEB)
Boettcher, Igor
2014-12-10
We investigate thermodynamics and phase structure of ultracold Fermi gases, which can be realized and measured in the laboratory with modern trapping techniques. We approach the subject from a both theoretical and experimental perspective. Central to the analysis is the systematic comparison of the BCS-BEC crossover of two-component fermions in both three and two dimensions. A dimensional reduction can be achieved in experiments by means of highly anisotropic traps. The Functional Renormalization Group (FRG) allows for a description of both cases in a unified theoretical framework. In three dimensions we discuss with the FRG the influence of high momentum particles onto the density, extend previous approaches to the Unitary Fermi Gas to reach quantitative precision, and study the breakdown of superfluidity due to an asymmetry in the population of the two fermion components. In this context we also investigate the stability of the Sarma phase. For the two-dimensional system scattering theory in reduced dimension plays an important role. We present both the theoretically as well as experimentally relevant aspects thereof. After a qualitative analysis of the phase diagram and the equation of state in two dimensions with the FRG we describe the experimental determination of the phase diagram of the two-dimensional BCS-BEC crossover in collaboration with the group of S. Jochim at PI Heidelberg.
Physics of ultracold Fermi gases revealed by spectroscopies
Törmä, Päivi
2016-04-01
This article provides a brief review of how various spectroscopies have been used to investitage many-body quantum phenomena in the context of ultracold Fermi gases. In particular, work done with RF spectroscopy, Bragg spectroscopy and lattice modulation spectroscopy is considered. The theoretical basis of these spectroscopies, namely linear response theory in the many-body quantum physics context is briefly presented. Experiments related to the BCS-BEC crossover, imbalanced Fermi gases, polarons, possible pseudogap and Fermi liquid behaviour and measuring the contact are discussed. Remaining open problems and goals in the field are sketched from the perspective how spectroscopies could contribute.
Vortex line in spin-orbit coupled atomic Fermi gases
2012-01-01
PHYSICAL REVIEW A 85, 013622 (2012) Vortex line in spin-orbit coupled atomic Fermi gases M. Iskin Department of Physics, Koc¸ University, Rumelifeneri Yolu, TR-34450 Sariyer, Istanbul, Turkey (Received 1 December 2011; published 17 January 2012) It has recently been shown that the spin-orbit coupling gives rise to topologically nontrivial and thermodynamically stable gapless superfluid phases when the pseudospin populations of an atomic Fermi gas are imbalanced, with the ...
Universality of the unitary Fermi gas: a few-body perspective
Levinsen, Jesper; Massignan, Pietro; Endo, Shimpei; Parish, Meera M.
2017-04-01
We revisit the properties of the two-component Fermi gas with short-range interactions in three dimensions, in the limit where the s-wave scattering length diverges. Such a unitary Fermi gas possesses universal thermodynamic and dynamical observables that are independent of any interaction length scale. Focusing on trapped systems of N fermions, where N≤slant 10, we investigate how well we can determine the zero-temperature behavior of the many-body system from published few-body data on the ground-state energy and the contact. For the unpolarized case, we find that the Bertsch parameters extracted from trapped few-body systems all lie within 15% of the established value. Furthermore, the few-body values for the contact are well within the range of values determined in the literature for the many-body system. In the limit of large spin polarization, we obtain a similar accuracy for the polaron energy, and we estimate the polaron’s effective mass from the dependence of its energy on N. We also compute an upper bound for the squared wave-function overlap between the unitary Fermi system and the non-interacting ground state, both for the trapped and uniform cases. This allows us to prove that the trapped unpolarized ground state at unitarity has zero overlap with its non-interacting counterpart in the many-body limit N\\to ∞ .
A phenomenological approach to the equation of state of a unitary Fermi gas
Indian Academy of Sciences (India)
M V N Murthy; M Brack; R K Bhaduri
2014-06-01
We propose a phenomenological approach for the equation of state of a unitary Fermi gas. The universal equation of state is parametrized in terms of Fermi–Dirac integrals. This reproduces the experimental data over the accessible range of fugacity and normalized temperature, but cannot describe the superfluid phase transition found in the MIT experiment [Ku et al, Science 335, 563 (2012)]. The most sensitive data for compressibility and specific heat at phase transition can, however, be fitted by introducing into the grand partition function a pair of complex conjugate zeros lying in the complex fugacity plane slightly off the real axis.
Superfluid Thomas—Fermi approximation for trapped fermi gases
Hernández, E. S.; Capuzzi, P.; Szybisz, L.
2009-02-01
We present a generalization of fermionic fluiddynamics to the case of two trapped fermion species with a contact interaction. Within a mean field approximation, we derive coupled equations of motion for the particle densities, particle currents, and anomalous pair density. For an inhomogeneous system, the equilibrium situation with vanishing currents is described by a generalized Thomas-Fermi relation that includes the superfluid gap, together with a new nonlocal gap equation that replaces the usual BCS one. These equations are numericaly solved resorting to a local density approximation (LDA). Density and gap profiles are analyzed in terms of the scattering length, revealing that the current frame can exhibit microscopic details of quantum origin that are frequently absent in more macroscopic scenarios.
Superfluid Thomas-Fermi approximation for trapped fermi gases
Energy Technology Data Exchange (ETDEWEB)
Hernandez, E S; Capuzzi, P; Szybisz, L [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, 1428 Buenos Aires (Argentina)], E-mail: shernand@df.uba.ar, E-mail: capuzzi@df.uba.ar, E-mail: szybisz@tandar.cnea.gov.ar
2009-02-01
We present a generalization of fermionic fluiddynamics to the case of two trapped fermion species with a contact interaction. Within a mean field approximation, we derive coupled equations of motion for the particle densities, particle currents, and anomalous pair density. For an inhomogeneous system, the equilibrium situation with vanishing currents is described by a generalized Thomas-Fermi relation that includes the superfluid gap, together with a new nonlocal gap equation that replaces the usual BCS one. These equations are numericaly solved resorting to a local density approximation (LDA). Density and gap profiles are analyzed in terms of the scattering length, revealing that the current frame can exhibit microscopic details of quantum origin that are frequently absent in more macroscopic scenarios.
Observation of the Efimovian expansion in scale-invariant Fermi gases
Deng, Shujin; Shi, Zhe-Yu; Diao, Pengpeng; Yu, Qianli; Zhai, Hui; Qi, Ran; Wu, Haibin
2016-07-01
Scale invariance plays an important role in unitary Fermi gases. Discrete scaling symmetry manifests itself in quantum few-body systems such as the Efimov effect. Here, we report on the theoretical prediction and experimental observation of a distinct type of expansion dynamics for scale-invariant quantum gases. When the frequency of the harmonic trap holding the gas decreases continuously as the inverse of time t, the expansion of the cloud size exhibits a sequence of plateaus. The locations of these plateaus obey a discrete geometric scaling law with a controllable scale factor, and the expansion dynamics is governed by a log-periodic function. This marked expansion shares the same scaling law and mathematical description as the Efimov effect.
Universal properties of Fermi gases in arbitrary dimensions
DEFF Research Database (Denmark)
Valiente, Manuel; T. Zinner, Nikolaj; Molmer, Klaus
2012-01-01
We consider spin-1/2 Fermi gases in arbitrary, integer or non-integer spatial dimensions, interacting via a Dirac delta potential. We first generalize the method of Tan's distributions and implement short-range boundary conditions to arbitrary dimension and we obtain a set of universal relations...... for the Fermi gas. Three-dimensional scattering under very general conditions of transversal confinement is described by an effectively reduced-dimensional scattering length, which we show depends on the three-dimensional scattering length in a universal way. Our formula for non-integer dimensions interpolates...
Review of pseudogaps in strongly interacting Fermi gases
Mueller, Erich J.
2017-10-01
A central challenge in modern condensed matter physics is developing the tools for understanding nontrivial yet unordered states of matter. One important idea to emerge in this context is that of a ‘pseudogap’: the fact that under appropriate circumstances the normal state displays a suppression of the single particle spectral density near the Fermi level, reminiscent of the gaps seen in ordered states of matter. While these concepts arose in a solid state context, they are now being explored in cold gases. This article reviews the current experimental and theoretical understanding of the normal state of strongly interacting Fermi gases, with particular focus on the phenomonology which is traditionally associated with the pseudogap.
Metastability of Bose and Fermi gases on the upper branch
LeClair, André; Roditi, Itzhak; Squires, Joshua
2016-12-01
We study three-dimensional Bose and Fermi gases in the upper branch, a phase defined by the absence of bound states in the repulsive interaction regime, within an approximation that considers only two-body interactions. Employing a formalism based on the S matrix, we derive useful analytic expressions that hold on the upper branch in the weak coupling limit. We determine upper branch phase diagrams for both bosons and fermions with techniques valid for arbitrary positive scattering length.
The unitary Fermi gas at finite temperature: momentum distribution and contact
Drut, Joaquín E; Ten, Timour
2011-01-01
The Unitary Fermi Gas (UFG) is one of the most strongly interacting systems known to date, as it saturates the unitarity bound on the quantum mechanical scattering cross section. The UFG corresponds to a two-component Fermi gas in the limit of short interaction range and large scattering length, and is currently realized in ultracold-atom experiments via Feshbach resonances. While easy to define, the UFG poses a challenging quantum many-body problem, as it lacks any characteristic scale other than the density. As a consequence, accurate quantitative predictions of the thermodynamic properties of the UFG require Monte Carlo calculations. However, significant progress has also been made with purely analytical methods. Notably, in 2005 Tan derived a set of exact thermodynamic relations in which a universal quantity known as the "contact" C plays a crucial role. Recently, C has also been found to determine the prefactor of the high- frequency power-law decay of correlators as well as the right-hand-sides of shear...
Universal properties of Fermi gases in arbitrary dimensions
Valiente, Manuel; Molmer, Klaus
2012-01-01
We consider spin-1/2 Fermi gases in arbitrary, integer or non-integer spatial dimensions, interacting via a Dirac delta potential. We first generalize the method of Tan's distributions and implement short-range boundary conditions to arbitrary dimension and we obtain a set of universal relations for the Fermi gas, which serve as dimensional interpolation/extrapolation formulae in between integer dimensions. We show that, under very general conditions, effective reduced-dimensional scattering lengths due to transversal confinement depend on the original three-dimensional scattering length in a universal way. As a direct consequence, we find that confinement-induced resonances occur in all dimensions different from D=2, without any need to solve the associated multichannel scattering problem. Finally, we show that reduced-dimensional contacts --- related to the tails of the momentum distributions --- are connected to the actual three-dimensional contact through a correction factor of purely geometric origin.
Finite-size Energy of Non-interacting Fermi Gases
Energy Technology Data Exchange (ETDEWEB)
Gebert, Martin, E-mail: gebert@math.lmu.de [ETH Zürich , Theoretische Physik (Switzerland)
2015-12-15
We study the asymptotics of the difference of the ground-state energies of two non-interacting N-particle Fermi gases in a finite volume of length L in the thermodynamic limit up to order 1/L. We are particularly interested in subdominant terms proportional to 1/L, called finite-size energy. In the nineties (Affleck, Nuc. Phys. B 58, 35–41 1997; Zagoskin and Affleck, J. Phys. A 30, 5743–5765 1997) claimed that the finite-size energy is related to the decay exponent occurring in Anderson’s orthogonality. We prove that the finite-size energy depends on the details of the thermodynamic limit and is therefore non-universal. Typically, it includes an additional linear term in the scattering phase shift.
Finite-size Energy of Non-interacting Fermi Gases
Gebert, Martin
2015-12-01
We study the asymptotics of the difference of the ground-state energies of two non-interacting N-particle Fermi gases in a finite volume of length L in the thermodynamic limit up to order 1/ L. We are particularly interested in subdominant terms proportional to 1/ L, called finite-size energy. In the nineties (Affleck, Nuc. Phys. B 58, 35-41 1997; Zagoskin and Affleck, J. Phys. A 30, 5743-5765 1997) claimed that the finite-size energy is related to the decay exponent occurring in Anderson's orthogonality. We prove that the finite-size energy depends on the details of the thermodynamic limit and is therefore non-universal. Typically, it includes an additional linear term in the scattering phase shift.
Beyond Gaussian pair fluctuation theory for strongly interacting Fermi gases
Mulkerin, Brendan C.; Liu, Xia-Ji; Hu, Hui
2016-07-01
Interacting Fermi systems in the strongly correlated regime play a fundamental role in many areas of physics and are of particular interest to the condensed matter community. Though weakly interacting fermions are understood, strongly correlated fermions are difficult to describe theoretically as there is no small interaction parameter to expand about. Existing strong-coupling theories rely heavily on the so-called many-body T -matrix approximation that sums ladder-type Feynman diagrams. Here, by acknowledging the fact that the effective interparticle interaction (i.e., the vertex function) becomes smaller above three dimensions, we propose an alternative way to reorganize Feynman diagrams and develop a theoretical framework for interacting Fermi gases beyond the ladder approximation. As an application, we solve the equation of state for three- and two-dimensional strongly interacting fermions and find excellent agreement with experimental [M. J. H. Ku et al., Science 335, 563 (2012), 10.1126/science.1214987] and other theoretical results above temperatures of 0.5 TF .
Transport phenomena in correlated quantum liquids: Ultracold Fermi gases and F/N junctions
Li, Hua
Landau Fermi-liquid theory was first introduced by L. D. Landau in the effort of understanding the normal state of Fermi systems, where the application of the concept of elementary excitations to the Fermi systems has proved very fruitful in clarifying the physics of strongly correlated quantum systems at low temperatures. In this thesis, I use Landau Fermi-liquid theory to study the transport phenomena of two different correlated quantum liquids: the strongly interacting ultracold Fermi gases and the ferromagnet/normal-metal (F/N) junctions. The detailed work is presented in chapter II and chapter III of this thesis, respectively. Chapter I holds the introductory part and the background knowledge of this thesis. In chapter II, I study the transport properties of a Fermi gas with strong attractive interactions close to the unitary limit. In particular, I compute the transport lifetimes of the Fermi gas due to superfluid fluctuations above the BCS transition temperature Tc. To calculate the transport lifetimes I need the scattering amplitudes. The scattering amplitudes are dominated by the superfluid fluctuations at temperatures just above Tc. The normal scattering amplitudes are calculated from the Landau parameters. These Landau parameters are obtained from the local version of the induced interaction model for computing Landau parameters. I also calculate the leading order finite temperature corrections to the various transport lifetimes. A calculation of the spin diffusion coefficient is presented in comparison to the experimental findings. Upon choosing a proper value of F0a, I am able to present a good match between the theoretical result and the experimental measurement, which indicates the presence of the superfluid fluctuations near Tc. Calculations of the viscosity, the viscosity/entropy ratio and the thermal conductivity are also shown in support of the appearance of the superfluid fluctuations. In chapter III, I study the spin transport in the low
Kharga, Digvijay; Tajima, Hiroyuki; van Wyk, Pieter; Inotani, Daisuke; Ohashi, Yoji
2017-07-01
We theoretically investigate normal-state properties of a unitary Bose-Fermi mixture. Including strong hetero-pairing fluctuations, we evaluate the Bose and Fermi chemical potential, internal energy, pressure, entropy, as well as specific heat at constant volume CV, within the framework of a combined strong-coupling theory with exact thermodynamic identities. We show that hetero-pairing fluctuations at the unitarity cause non-monotonic temperature dependence of CV, being qualitatively different from the monotonic behavior of this quantity in the weak- and strong-coupling limit. On the other hand, such an anomalous behavior is not seen in the other quantities. Our results indicate that the specific heat CV, which has recently become observable in cold atom physics, is a useful quantity for understanding strong-coupling aspects of this quantum system.
Microscopy of 2D Fermi gases. Exploring excitations and thermodynamics
Energy Technology Data Exchange (ETDEWEB)
Morgener, Kai Henning
2014-12-08
This thesis presents experiments on three-dimensional (3D) and two-dimensional (2D) ultracold fermionic {sup 6}Li gases providing local access to microscopic quantum many-body physics. A broad magnetic Feshbach resonance is used to tune the interparticle interaction strength freely to address the entire crossover between the Bose-Einstein-Condensate (BEC) and Bardeen-Cooper-Schrieffer (BCS) regime. We map out the critical velocity in the crossover from BEC to BCS superfluidity by moving a small attractive potential through the 3D cloud. We compare the results with theoretical predictions and achieve quantitative understanding in the BEC regime by performing numerical simulations. Of particular interest is the regime of strong correlations, where no theoretical predictions exist. In the BEC regime, the critical velocity should be closely related to the speed of sound, according to the Landau criterion and Bogolyubov theory. We measure the sound velocity by exciting a density wave and tracking its propagation. The focus of this thesis is on our first experiments on general properties of quasi-2D Fermi gases. We realize strong vertical confinement by generating a 1D optical lattice by intersecting two blue-detuned laser beams under a steep angle. The large resulting lattice spacing enables us to prepare a single planar quantum gas deeply in the 2D regime. The first measurements of the speed of sound in quasi-2D gases in the BEC-BCS crossover are presented. In addition, we present preliminary results on the pressure equation of state, which is extracted from in-situ density profiles. Since the sound velocity is directly connected to the equation of state, the results provide a crosscheck of the speed of sound. Moreover, we benchmark the derived sound from available equation of state predictions, find very good agreement with recent numerical calculations, and disprove a sophisticated mean field approach. These studies are carried out with a novel apparatus which has
Observation of the Leggett-Rice effect in a unitary Fermi gas.
Trotzky, S; Beattie, S; Luciuk, C; Smale, S; Bardon, A B; Enss, T; Taylor, E; Zhang, S; Thywissen, J H
2015-01-09
We observe that the diffusive spin current in a strongly interacting degenerate Fermi gas of (40)K precesses about the local magnetization. As predicted by Leggett and Rice, precession is observed both in the Ramsey phase of a spin-echo sequence, and in the nonlinearity of the magnetization decay. At unitarity, we measure a Leggett-Rice parameter γ=1.08(9) and a bare transverse spin diffusivity D(0)(⊥)=2.3(4)ℏ/m for a normal-state gas initialized with full polarization and at one-fifth of the Fermi temperature, where m is the atomic mass. One might expect γ=0 at unitarity, where two-body scattering is purely dissipative. We observe γ→0 as temperature is increased towards the Fermi temperature, consistent with calculations that show the degenerate Fermi sea restores a nonzero γ. Tuning the scattering length a, we find that a sign change in γ occurs in the range 0Fermi momentum. We discuss how γ reveals the effective interaction strength of the gas, such that the sign change in γ indicates a switching of branch between a repulsive and an attractive Fermi gas.
Population and mass imbalance in atomic Fermi gases
Baarsma, J E; Gubbels, K.B.; Stoof, H.T.C.
2010-01-01
We develop an accurate theory of resonantly interacting Fermi mixtures with both spin and mass imbalance. We consider Fermi mixtures with arbitrary mass imbalances but focus, in particular, on the experimentally available Li6-K40 mixture. We determine the phase diagram of the mixture for different i
Physics of our Days: Cooling and thermometry of atomic Fermi gases
Onofrio, R.
2017-02-01
We review the status of cooling techniques aimed at achieving the deepest quantum degeneracy for atomic Fermi gases. We first discuss some physics motivations, providing a quantitative assessment of the need for deep quantum degeneracy in relevant physics cases, such as the search for unconventional superfluid states. Attention is then focused on the most widespread technique to reach deep quantum degeneracy for Fermi systems, sympathetic cooling of Bose–Fermi mixtures, organizing the discussion according to the specific species involved. Various proposals to circumvent some of the limitations on achieving the deepest Fermi degeneracy, and their experimental realizations, are then reviewed. Finally, we discuss the extension of these techniques to optical lattices and the implementation of precision thermometry crucial to the understanding of the phase diagram of classical and quantum phase transitions in Fermi gases.
String Theory Based Predictions for Novel Collective Modes in Strongly Interacting Fermi Gases
Bantilan, H; Ishii, T; Lewis, W E; Romatschke, P
2016-01-01
Very different strongly interacting quantum systems such as Fermi gases, quark-gluon plasmas formed in high energy ion collisions and black holes studied theoretically in string theory are known to exhibit quantitatively similar damping of hydrodynamic modes. It is not known if such similarities extend beyond the hydrodynamic limit. Do non-hydrodynamic collective modes in Fermi gases with strong interactions also match those from string theory calculations? In order to answer this question, we use calculations based on string theory to make predictions for novel types of modes outside the hydrodynamic regime in trapped Fermi gases. These predictions are amenable to direct testing with current state-of-the-art cold atom experiments.
Magnetostriction and exchange effects in trapped dipolar Bose and Fermi gases
Baillie, D; Blakie, P. B.
2012-01-01
We examine the magnetostrictive position and momentum space distortions that occur in harmonically confined dipolar Bose and Fermi gases. Direct interactions give rise to position space magnetostriction and exchange interactions give rise to momentum space magnetostriction. While the position space magnetostriction is similar in Bose and Fermi systems, the momentum space magnetostriction is markedly different: the Bose gas momentum distribution distorts in the opposite sense to that of the Fe...
Metastability in spin polarised Fermi gases and quasiparticle decays
DEFF Research Database (Denmark)
Sadeghzadeh, Kayvan; Bruun, Georg; Lobo, Carlos
2011-01-01
the interaction strength at which a polarised phase of molecules becomes the groundstate, to the one at which the single quasiparticle groundstate changes character from polaronic to molecular. Our argument in terms of a Fermi sea of polarons naturally suggests their use as an experimental probe. We propose...
Repulsive polarons and itinerant ferromagnetism in strongly polarized Fermi gases
DEFF Research Database (Denmark)
Massignan, Pietro; Bruun, Georg
2011-01-01
We analyze the properties of a single impurity immersed in a Fermi sea. At positive energy and scattering lengths, we show that the system possesses a well-defined but metastable excitation, the repulsive polaron, and we calculate its energy, quasiparticle residue and effective mass. From a therm...
Correlations of the upper branch of 1D harmonically trapped two-component fermi gases.
Gharashi, Seyed Ebrahim; Blume, D
2013-07-26
We present highly accurate energy spectra and eigenfunctions of small 1D harmonically trapped two-component Fermi gases with interspecies δ-function interactions, and analyze the correlations of the so-called upper branch (i.e., the branch that describes a repulsive Fermi gas consisting of atoms but no molecules) for positive and negative coupling constants. Changes of the two-body correlations as a function of the interspecies coupling strength reflect the competition of the interspecies interaction and the effective repulsion due to the Pauli exclusion principle, and are interpreted as a few-body analog of a transition from a nonmagnetic to a magnetic phase. Moreover, we show that the eigenstate ψadia of the infinitely strongly interacting system with |n1+n2|>2 and |n1-n2|Fermi-Fermi mapping function to the eigenfunction of the noninteracting single-component Fermi gas.
Nonlinear Ramsey Interferometry of Fermi Superfluid Gases in a Double-Well Potential
Institute of Scientific and Technical Information of China (English)
蒙红娟; 苟学强; 王文元; 杨阳; 段文山
2012-01-01
The nonlinear Ramsey interferometry of Fermi superfluid gases in a double-well potential is investigated in this paper. We found that the frequency of the Ramsey fringes exactly reflects the strength of nonlinearity, or the scattering length of the Fermi superfluid gases. The cases of sudden limit, the adiabatic limit and the general case are studied. The analytical result is in good agreement with the numerical ones. The adiabatic condition is proposed. In general situation, the zero-frequency point emerge. Finally the possible applications of the theory axe discussed.
Collective Modes in a Unitary Fermi Gas across the Superfluid Phase Transition
Tey, Meng Khoon; Sidorenkov, Leonid A.; Guajardo, Edmundo R. Sánchez; Grimm, Rudolf; Ku, Mark J. H.; Zwierlein, Martin W.; Hou, Yan-Hua; Pitaevskii, Lev; Stringari, Sandro
2013-02-01
We provide a joint theoretical and experimental investigation of the temperature dependence of the collective oscillations of first sound nature exhibited by a highly elongated harmonically trapped Fermi gas at unitarity, including the region below the critical temperature for superfluidity. Differently from the lowest axial breathing mode, the hydrodynamic frequencies of the higher-nodal excitations show a temperature dependence, which is calculated starting from Landau two-fluid theory and using the available experimental knowledge of the equation of state. The experimental results agree with high accuracy with the predictions of theory and provide the first evidence for the temperature dependence of the collective frequencies near the superfluid phase transition.
Effective-range dependence of two-dimensional Fermi gases
Schonenberg, L. M.; Verpoort, P. C.; Conduit, G. J.
2017-08-01
The Feshbach resonance provides precise control over the scattering length and effective range of interactions between ultracold atoms. We propose the ultratransferable pseudopotential to model effective interaction ranges -1.5 ≤kF2Reff2≤0 , where Reff is the effective range and kF is the Fermi wave vector, describing narrow to broad Feshbach resonances. We develop a mean-field treatment and exploit the pseudopotential to perform a variational and diffusion Monte Carlo study of the ground state of the two-dimensional Fermi gas, reporting on the ground-state energy, contact, condensate fraction, momentum distribution, and pair-correlation functions as a function of the effective interaction range across the BEC-BCS crossover. The limit kF2Reff2→-∞ is a gas of bosons with zero binding energy, whereas ln(kFa )→-∞ corresponds to noninteracting bosons with infinite binding energy.
Thermodynamic characteristics of Fermi gases in a magnetic field
Energy Technology Data Exchange (ETDEWEB)
Lipovetskii, S.S.; Olesik, A.A.; Sekerzhitskii, V.S.
1987-11-01
Within the framework of statistical thermodynamics of equilibrium systems, general expressions are obtained for the chemical potential, pressure, and magnetic susceptibility for degenerate ideal nonrelativistic electron, proton, and neutron gases in magnetic fields, which exert no pronounced influence on the anomalous magnetic moments of the fermions.
Korteweg de Vries Description of One-Dimensional Superfluid Fermi Gases
Institute of Scientific and Technical Information of China (English)
徐艳霞; 段文山
2011-01-01
We study one-dimensional matter-wave pulses in cigar-shaped superfluid Fermi gases, including the linear and nonlinear waves of the system. A Korteweg de Vries (KdV) solitary wave is obtained for the superfluid Fermi gases in the limited case of a BEC regime, a BCS regime and unitarity. The dependences of the propagation velocity, amplitude and the width of the solitary wave on the dimensionless interaction parameter y = 1/{kFasc) are given for the limited cases of BEC and unitarity.%We study one-dimensional matter-wave pulses in cigar-shaped superfluid Fermi gases,including the linear and nonlinear waves of the system.A Korteweg de Vries(KdV)solitary wave is obtained for the superfluid Fermi gases in the limited case of a BEC regime,a BCS regime and unitarity.The dependences of the propagation velocity,amplitude and the width of the solitary wave on the dimensionless interaction parameter y =1 /(kFasc)are given for the limited cases of BEC and unitarity.
Transdimensional equivalence of universal constants for Fermi gases at unitarity.
Endres, Michael G
2012-12-21
I present lattice Monte Carlo calculations for a universal four-component Fermi gas confined to a finite box and to a harmonic trap in one spatial dimension. I obtain the values ξ(1D) = 0.370(4) and ξ(1D) = 0.372(1), respectively, for the Bertsch parameter, a nonperturbative universal constant defined as the (square of the) energy of the untrapped (trapped) system measured in units of the free gas energy. The Bertsch parameter obtained for the one-dimensional system is consistent to within ~1% uncertainties with the most recent numerical and experimental estimates of the analogous Bertsch parameter for a three-dimensional spin-1/2 Fermi gas at unitarity. The finding suggests the intriguing possibility that there exists a universality between two conformal theories in different dimensions. To lend support to this study, I also compute ground state energies for four and five fermions confined to a harmonic trap and demonstrate the restoration of a virial theorem in the continuum limit. The continuum few-body energies obtained are consistent with exact analytical calculations to within ~1.0% and ~0.3% statistical uncertainties, respectively.
Transdimensional equivalence of universal constants from universal Fermi gases
Endres, Michael G
2012-01-01
I present lattice Monte Carlo calculations for a universal four-component Fermi gas confined to a finite box and to a harmonic trap in one spatial dimension. I obtain the continuum and thermodynamic limit extrapolated values xi_1d = 0.370(4) and xi_1d = 0.372(1), respectively, for the Bertsch parameter, a nonperturbative universal constant defined as the (square of the) energy of the untrapped (trapped) system measured in units of the free gas energy. The Bertsch parameter for the one-dimensional system is consistent to within ~1% uncertainties with the most recent numerical and experimental estimates of the analogous Bertsch parameter for a three-dimensional spin-1/2 Fermi gas at unitarity. The finding suggests the intriguing possibility that there exists a universality between two conformal theories in different dimensions. To lend support to this study, I also compute continuum extrapolated ground state energies for four and five fermions confined to a harmonic trap and demonstrate the restoration of a Vir...
Energy Technology Data Exchange (ETDEWEB)
Tempere, J., E-mail: jacques.tempere@ua.ac.b [TQC, Universiteit Antwerpen, B-2020 Antwerpen (Belgium); Lyman Laboratory of Physics, Harvard University, Cambridge, MA 02138 (United States); Klimin, S.N. [TQC, Universiteit Antwerpen, B-2020 Antwerpen (Belgium); Dept. of Theoretical Physics, State University of Moldova, MD-2009 Chisinau (Moldova, Republic of); Devreese, J.T. [TQC, Universiteit Antwerpen, B-2020 Antwerpen (Belgium); COBRA, Eindhoven University of Technology, 5600 MB Eindhoven (Netherlands)
2010-10-01
The physics of two-dimensional (2D) quantum gases can be revealed in strongly confining optical lattices. Upon cooling, 2D bosonic quantum gases as well as Fermi gases where pairing is present, become superfluid. The superfluid-to-normal transition is no longer governed by the presence or absence of a condensate, but by the Berezinskii-Kosterlitz-Thouless (BKT) mechanism: above a critical temperature, vortices and antivortices proliferate and destroy phase coherence. We investigate the BKT transition for superfluid 2D Fermi gases in the whole range of the BCS-BEC crossover, from weakly bound Cooper pairing (the BCS state), up to strongly bound molecules (the BEC state). Using a path-integral description, we then focus on the case of imbalanced gases: when the number of 'spin-up' and 'spin-down' fermions that form the pair is no longer equal. When an excess of one spin species exists, pairing is frustrated and the vortex energetics is strongly affected, influencing the KT mechanism. In the present work we are concentrated on the effect of both phase and amplitude fluctuations on phase diagrams of the fermion system. The amplitude fluctuations only slightly influence the BKT phase transition temperature. However, they lead to a substantial modification of the complete phase diagram for the Fermi gas in 2D with respect to that obtained taking into account only phase fluctuations.
Phase Transitions in Definite Total Spin States of Two-Component Fermi Gases.
Yurovsky, Vladimir A
2017-05-19
Second-order phase transitions have no latent heat and are characterized by a change in symmetry. In addition to the conventional symmetric and antisymmetric states under permutations of bosons and fermions, mathematical group-representation theory allows for non-Abelian permutation symmetry. Such symmetry can be hidden in states with defined total spins of spinor gases, which can be formed in optical cavities. The present work shows that the symmetry reveals itself in spin-independent or coordinate-independent properties of these gases, namely as non-Abelian entropy in thermodynamic properties. In weakly interacting Fermi gases, two phases appear associated with fermionic and non-Abelian symmetry under permutations of particle states, respectively. The second-order transitions between the phases are characterized by discontinuities in specific heat. Unlike other phase transitions, the present ones are not caused by interactions and can appear even in ideal gases. Similar effects in Bose gases and strong interactions are discussed.
Localization of interacting Fermi gases in quasiperiodic potentials
Pilati, Sebastiano; Varma, Vipin Kerala
2017-01-01
We investigate the zero-temperature metal-insulator transition in a one-dimensional two-component Fermi gas in the presence of a quasiperiodic potential resulting from the superposition of two optical lattices of equal intensity but incommensurate periods. A mobility edge separating (low-energy) Anderson localized and (high-energy) extended single-particle states appears in this continuous-space model beyond a critical intensity of the quasiperiodic potential. To discern the metallic phase from the insulating phase in the interacting many-fermion system, we employ unbiased quantum Monte Carlo (QMC) simulations combined with the many-particle localization length familiar from the modern theory of the insulating state. In the noninteracting limit, the critical optical-lattice intensity for the metal-insulator transition predicted by the QMC simulations coincides with the Anderson localization transition of the single-particle eigenstates. We show that weak repulsive interactions induce a shift of this critical point towards larger intensities, meaning that repulsion favors metallic behavior. This shift appears to be linear in the interaction parameter, suggesting that even infinitesimal interactions can affect the position of the critical point.
Yan, Yangqian; Blume, D
2016-06-10
The unitary equal-mass Fermi gas with zero-range interactions constitutes a paradigmatic model system that is relevant to atomic, condensed matter, nuclear, particle, and astrophysics. This work determines the fourth-order virial coefficient b_{4} of such a strongly interacting Fermi gas using a customized ab initio path-integral Monte Carlo (PIMC) algorithm. In contrast to earlier theoretical results, which disagreed on the sign and magnitude of b_{4}, our b_{4} agrees within error bars with the experimentally determined value, thereby resolving an ongoing literature debate. Utilizing a trap regulator, our PIMC approach determines the fourth-order virial coefficient by directly sampling the partition function. An on-the-fly antisymmetrization avoids the Thomas collapse and, combined with the use of the exact two-body zero-range propagator, establishes an efficient general means to treat small Fermi systems with zero-range interactions.
Composite-boson approach to molecular Bose-Einstein condensates in mixtures of ultracold Fermi gases
Bouvrie, P. Alexander; Tichy, Malte C.; Roditi, Itzhak
2017-02-01
We show that an ansatz based on independent composite bosons [Phys. Rep. 463, 215 (2008), 10.1016/j.physrep.2007.11.003] accurately describes the condensate fraction of molecular Bose-Einstein condensates in ultracold Fermi gases. The entanglement between the fermionic constituents of a single Feshbach molecule then governs the many-particle statistics of the condensate, from the limit of strong interaction to close to unitarity. This result strengthens the role of entanglement as the indispensable driver of composite-boson behavior. The condensate fraction of fermion pairs at zero temperature that we compute matches excellently previous results obtained by means of fixed-node diffusion Monte Carlo methods and the Bogoliubov depletion approximation. This paves the way towards the exploration of the BEC-BCS crossover physics in mixtures of cold Fermi gases with an arbitrary number of fermion pairs as well as the implementation of Hong-Ou-Mandel-like interference experiments proposed within coboson theory.
Thermodynamic equivalence of two-dimensional imperfect attractive Fermi and repulsive Bose gases
Napiórkowski, Marek; Piasecki, Jarosław
2017-06-01
We consider two-dimensional imperfect attractive Fermi and repulsive Bose gases consisting of spinless point particles whose total interparticle interaction energy is represented by a N2/2 V with a =-aF≤0 for fermions and a =aB≥0 for bosons. We show that, in spite of the attraction, the thermodynamics of a d =2 imperfect Fermi gas remains well defined for 0 ≤aF≤a0=h2/2 π m , and is exactly the same as the one of the repulsive imperfect Bose gas with aB=a0-aF . In particular, for aF=a0 one observes the thermodynamic equivalence of the attractive imperfect Fermi gas and the ideal Bose gas.
Institute of Scientific and Technical Information of China (English)
YANGXiao－Xue; WUYing
2002-01-01
We develop a simple approach to obtain explicitly exact analytical expressions of particle and kineticenergy densities for noninteracting Fermi gases in one-dimensional harmonic confinement,and in one-dimensional box confinement as well.
Institute of Scientific and Technical Information of China (English)
YANG XiaoXue; WU Ying
2002-01-01
We develop a simple approach to obtain explicitly exact analytical expressions of particle and kinetic-energy densities for noninteracting Fermi gases in one-dimensional harmonic confinement, and in one-dimensional boxconfinement as well.
Theoretical studies of Efimov states and dynamics in quenched unitary Bose gases
D'Incao, Jose P.; Wang, Jia; Klauss, Cathy; Xie, Xin; Jin, Deborah S.; Cornell, Eric A.
2016-05-01
We study the three-body physics relevant for quenched unitary Bose gas experiments in order to determine the role of Efimov states on the dynamics of the atomic and molecular populations. Initially, the interatomic interactions are quenched from weak to infinitely strong. After some dwelling time, the interactions are slowly ramped back to some final weak value where a mixture of atoms, dimers, and Efimov trimers can exist and whose populations depend strongly on the dwell time. We model the problem using the adiabatic hyperspherical representation for three atoms assuming a local interaction model in which a harmonic potential mimics finite density effects. We also developed a novel Slow Variable Discretization (SVD) method to accurately determine the time evolution of the system, overcoming the difficulty of implementing diabatization schemes to minimize unwanted effects due to sharp-avoid crossings. This method also allows us to account for three-body losses during the time evolution. This research is supported by the U. S. National Science Foundation.
Phase transitions in definite total spin states of two-component Fermi gases
Yurovsky, Vladimir A
2016-01-01
Symmetry under permutations of indistinguishable particles, contained in each medium, is one of the fundamental symmetries. Generally, a change in symmetry affects the medium's thermodynamic properties, leading to phase transitions. Permutation symmetry can be changed since, in addition to the conventional symmetric and anti-symmetric states under permutations of bosons and fermions, mathematical group-representation theory allows for non-Abelian permutation symmetry. Such symmetry can be hidden in states with defined total spins of spinor gases, which can be formed in optical cavities. However, the thermodynamic effects of non-Abelian symmetry are unknown. The present work shows that the symmetry reveals itself in spin-independent or coordinate-independent properties of these gases, namely as non-Abelian entropy in thermodynamic properties. In weakly interacting Fermi gases, saturated and unsaturated phases appear associated with fermionic and non-Abelian symmetry under permutations of particle states, respe...
Polaronic atom-trimer continuity in three-component Fermi gases.
Nishida, Yusuke
2015-03-20
Recently it has been proposed that three-component Fermi gases may exhibit a new type of crossover physics in which an unpaired Fermi sea of atoms smoothly evolves into that of trimers in addition to the ordinary BCS-BEC crossover of condensed pairs. Here we study its corresponding polaron problem in which a single impurity atom of one component interacts with condensed pairs of the other two components with equal populations. By developing a variational approach in the vicinity of a narrow Feshbach resonance, we show that the impurity atom smoothly changes its character from atom to trimer with increasing the attraction and eventually there is a sharp transition to dimer. The emergent polaronic atom-trimer continuity can be probed in ultracold atoms experiments by measuring the impurity spectral function. Our novel crossover wave function properly incorporating the polaronic atom-trimer continuity will provide a useful basis to further investigate the phase diagram of three-component Fermi gases in more general situations.
Extension of the Ginzburg–Landau approach for ultracold Fermi gases below a critical temperature
Energy Technology Data Exchange (ETDEWEB)
Klimin, S.N., E-mail: sergei.klimin@ua.ac.be [Theorie van Kwantumsystemen en Complexe Systemen (TQC), Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen (Belgium); Tempere, J., E-mail: jacques.tempere@uantwerpen.be [Theorie van Kwantumsystemen en Complexe Systemen (TQC), Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen (Belgium); Lyman Laboratory of Physics, Harvard University, Cambridge, MA 02138 (United States); Devreese, J.T. [Theorie van Kwantumsystemen en Complexe Systemen (TQC), Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen (Belgium)
2014-08-15
Highlights: • Ginzburg–Landau formalism is extended below the critical temperature. • Two different healing lengths in two-band superfluids are captured. • The developed method is focused on strong-coupling superfluid Fermi gases. - Abstract: In the context of superfluid Fermi gases, the Ginzburg–Landau (GL) formalism for the macroscopic wave function has been successfully extended to the whole temperature range where the superfluid state exists. After reviewing the formalism, we first investigate the temperature-dependent correction to the standard GL expansion (which is valid close to T{sub c}). Deviations from the standard GL formalism are particularly important for the kinetic energy contribution to the GL energy functional, which in turn influences the healing length of the macroscopic wave function. We apply the formalism to variationally describe vortices in a strong-coupling Fermi gas in the BEC–BCS crossover regime, in a two-band system. The healing lengths, derived as variational parameters in the vortex wave function, are shown to exhibit hidden criticality well below T{sub c}.
Kvashnin, A Yu; Yushkanov, A A
2012-01-01
The classical Kramers problem of the kinetic theory is solved. The Kramers problem about isothermal sliding for quantum Fermi gases is considered. Quantum gases with the velocity - dependent collision frequency are considered. Specular - diffusive boundary conditions are applied. Dependence of isothermal sliding on the resulted chemical potential is found out.
Ultracold Fermi and Bose gases and Spinless Bose Charged Sound Particles
Directory of Open Access Journals (Sweden)
Minasyan V.
2011-10-01
Full Text Available We propose a novel approach for investigation of the motion of Bose or Fermi liquid (or gas which consists of decoupled electrons and ions in the uppermost hyperfine state. Hence, we use such a concept as the fluctuation motion of “charged fluid particles” or “charged fluid points” representing a charged longitudinal elastic wave. In turn, this elastic wave is quantized by spinless longitudinal Bose charged sound particles with the rest mass m and charge e 0 . The existence of spinless Bose charged sound particles allows us to present a new model for description of Bose or Fermi liquid via a non-ideal Bose gas of charged sound particles . In this respect, we introduce a new postulation for the superfluid component of Bose or Fermi liquid determined by means of charged sound particles in the condensate, which may explain the results of experiments connected with ultra-cold Fermi gases of spin-polarized hydrogen, 6 Li and 40 K, and such a Bose gas as 87 Rb in the uppermost hyperfine state, where the Bose- Einstein condensation of charged sound particles is realized by tuning the magnetic field.
George E. Valley, Jr. Prize Talk: Exact relations for Fermi gases with large scattering length
Tan, Shina
2011-05-01
Ultracold two-component atomic Fermi gases near broad Feshbach resonances have both strong interactions and relatively long life times, and the strong attractions between fermions lead to remarkable properties such as superfluidity at large percentages of the Fermi temperature. The interactions can often be described by a single parameter, the two-body s-wave scattering length, which determines how the many-body wave function behaves as two atoms get much closer than the average interparticle spacing. This short-range structure of the wave function leads to a number of exact relations among energy, momentum distribution, pressure, and various high-frequency and short-wave properties. All the relations involve a quantity called contact. The exact relations point to a number of independent determinations of the contact, which have been beautifully demonstrated experimentally as well as numerically. This work was supported, in part, by DOE Grant No. DE-FG02-00ER41132.
Time-of-flight expansion of trapped dipolar Fermi gases: from collisionless to hydrodynamic regime
Veljic, Vladimir; Pelster, Axel
2016-01-01
A recent time-of-flight (TOF) expansion experiment with polarized fermionic erbium atoms measured a Fermi surface deformation from a sphere to an ellipsoid due to dipole-dipole interaction, thus confirming previous theoretical predictions. Here we perform a systematic study of the ground-state properties and TOF dynamics for trapped dipolar Fermi gases from the collisionless to the hydrodynamic regime at zero temperature. To this end we solve analytically the underlying Boltzmann-Vlasov equation within the relaxation-time approximation in the vicinity of equilibrium by using a suitable rescaling of the equilibrium distribution. The resulting ordinary differential equations for the respective scaling parameters are then solved numerically for experimentally realistic parameters and relaxation times that correspond to the collisionless, collisional, and hydrodynamic regime. The equations for the collisional regime are first solved in the approximation of a fixed relaxation time, and then this approach is extend...
Perturbative thermodynamic geometry of nonextensive ideal classical, Bose, and Fermi gases.
Mohammadzadeh, Hosein; Adli, Fereshteh; Nouri, Sahereh
2016-12-01
We investigate perturbative thermodynamic geometry of nonextensive ideal classical, Bose, and Fermi gases. We show that the intrinsic statistical interaction of nonextensive Bose (Fermi) gas is attractive (repulsive) similar to the extensive case but the value of thermodynamic curvature is changed by a nonextensive parameter. In contrary to the extensive ideal classical gas, the nonextensive one may be divided to two different regimes. According to the deviation parameter of the system to the nonextensive case, one can find a special value of fugacity, z^{*}, where the sign of thermodynamic curvature is changed. Therefore, we argue that the nonextensive parameter induces an attractive (repulsive) statistical interaction for zz^{*}) for an ideal classical gas. Also, according to the singular point of thermodynamic curvature, we consider the condensation of nonextensive Boson gas.
All-optical cooling of Fermi gases via Pauli inhibition of spontaneous emission
Onofrio, Roberto
2016-01-01
A technique is proposed to cool Fermi gases to the regime of quantum degeneracy based on the expected inhibition of spontaneous emission due to the Pauli principle. The reduction of the linewidth for spontaneous emission originates a corresponding reduction of the Doppler temperature, which under specific conditions may give rise to a runaway process through which fermions are progressively cooled. The approach requires a combination of a magneto-optical trap as a cooling system and an optical dipole trap to enhance quantum degeneracy. This results in expected Fermi degeneracy factors $T/T_F$ comparable to the lowest values recently achieved, with potential for a direct implementation in optical lattices. The experimental demonstration of this technique should also indirectly provide a macroscopic manifestation of the Pauli exclusion principle at the atomic physics level.
Interacting Bose and Fermi Gases in Low Dimensions and the Riemann Hypothesis
Leclair, André
We apply the S-matrix based finite temperature formalism to nonrelativistic Bose and Fermi gases in 1+1 and 2+1 dimensions. For the (2+1)-dimensional case in the constant scattering length approximation, the free energy is given in terms of Roger's dilogarithm in a way analagous to the thermodynamic Bethe ansatz for the relativistic (1+1)-dimensional case. The 1d fermionic case with a quasiperiodic two-body potential is closely connected with the Riemann hypothesis.
Wang, Jibiao; Che, Yanming; Zhang, Leifeng; Chen, Qijin
2017-01-01
Ultracold two-component Fermi gases with a tunable population imbalance have provided an excellent opportunity for studying the exotic Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states, which have been of great interest in condensed matter physics. However, the FFLO states have not been observed experimentally in Fermi gases in three dimensions (3D), possibly due to their small phase space volume and extremely low temperature required for an equal-mass Fermi gas. Here we explore possible effects of mass imbalance, mainly in a 6Li–40K mixture, on the one-plane-wave FFLO phases for a 3D homogeneous case at the mean-field level. We present various phase diagrams related to the FFLO states at both zero and finite temperatures, throughout the BCS-BEC crossover, and show that a large mass ratio may enhance substantially FFLO type of pairing.
Wang, Jibiao; Che, Yanming; Zhang, Leifeng; Chen, Qijin
2017-01-01
Ultracold two-component Fermi gases with a tunable population imbalance have provided an excellent opportunity for studying the exotic Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states, which have been of great interest in condensed matter physics. However, the FFLO states have not been observed experimentally in Fermi gases in three dimensions (3D), possibly due to their small phase space volume and extremely low temperature required for an equal-mass Fermi gas. Here we explore possible effects of mass imbalance, mainly in a 6Li–40K mixture, on the one-plane-wave FFLO phases for a 3D homogeneous case at the mean-field level. We present various phase diagrams related to the FFLO states at both zero and finite temperatures, throughout the BCS-BEC crossover, and show that a large mass ratio may enhance substantially FFLO type of pairing. PMID:28051145
Superfluidity and BCS-BEC crossover of ultracold atomic Fermi gases in mixed dimensions
Zhang, Leifeng; Chen, Qijin
Atomic Fermi gases have been under active investigation in the past decade. Here we study the superfluid and pairing phenomena of a two-component ultracold atomic Fermi gas in the presence of mixed dimensionality, in which one component is confined on a 1D optical lattice whereas the other is free in the 3D continuum. We assume a short-range pairing interaction and determine the superfluid transition temperature Tc and the phase diagram for the entire BCS-BEC crossover, using a pairing fluctuation theory which includes self-consistently the contributions of finite momentum pairs. We find that, as the lattice depth increases and the lattice spacing decreases, the behavior of Tc becomes very similar to that of a population imbalance Fermi gas in a simple 3D continuum. There is no superfluidity even at T = 0 below certain threshold of pairing strength in the BCS regime. Nonmonotonic Tc behavior and intermediate temperature superfluidity emerge, and for deep enough lattice, the Tc curve will split into two parts. Implications for experiment will be discussed. References: 1. Q.J. Chen, Ioan Kosztin, B. Janko, and K. Levin, Phys. Rev. B 59, 7083 (1999). 2. Chih-Chun Chien, Qijin Chen, Yan He, and K. Levin, Phys. Rev. Lett. 97, 090402(2006). Work supported by NSF of China and the National Basic Research Program of China.
Single-particle-excitation spectrum of degenerate Fermi gases in a ring cavity
Feng, Chao; Chen, Yu
2017-09-01
By considering spin-1/2 degenerate Fermi gases in a ring cavity where strong interaction between atoms and light gives rise to superradiance, we find that the cavity dissipation can cause a severe broadening in some special cases, breaking down the quasiparticle picture which has been constantly assumed in mean-field theory studies. This broadening happens when the band gap is resonant with polariton excitation energy. Interestingly enough, this broadening is highly spin selective, depending on how the fermions are filled, and the spectrum becomes asymmetric due to dissipation. Further, a nonmonotonous dependence of the maximal broadening of the spectrum on the cavity decay rate κ is found and the largest broadening emerges at κ , comparable to the recoil energy.
Tan's contact and the phase distribution of repulsive Fermi gases: Insights from QCD noise analyses
Porter, William J
2016-01-01
Path-integral analyses originally pioneered in the study of the complex-phase problem afflicting lattice calculations of finite-density quantum chromodynamics are generalized to non-relativistic Fermi gases with repulsive interactions. Using arguments similar to those previously applied to relativistic theories, we show that the analogous problem in nonrelativistic systems manifests itself naturally in Tan's contact as a nontrivial cancellation between terms with varied dependence on extensive thermodynamic quantities. We analyze that case under the assumption of gaussian phase distribution, which is supported by our Monte Carlo calculations and perturbative considerations. We further generalize these results to observables other than the contact, as well as to polarized systems and systems with fixed particle number. Our results are quite general in that they apply to repulsive multi-component fermions, are independent of dimensionality or trapping potential, and hold in the ground state as well as at finite...
Directory of Open Access Journals (Sweden)
Hao Guo
2015-01-01
Full Text Available Recent experimental progress allows for exploring some important physical quantities of ultracold Fermi gases, such as the compressibility, spin susceptibility, viscosity, optical conductivity, and spin diffusivity. Theoretically, these quantities can be evaluated from suitable linear response theories. For BCS superfluid, it has been found that the gauge invariant linear response theories can be fully consistent with some stringent consistency constraints. When the theory is generalized to stronger than BCS regime, one may meet serious difficulties to satisfy the gauge invariance conditions. In this paper, we try to construct density and spin linear response theories which are formally gauge invariant for a Fermi gas undergoing BCS-Bose-Einstein Condensation (BEC crossover, especially below the superfluid transition temperature Tc. We adapt a particular t-matrix approach which is close to the G0G formalism to incorporate noncondensed pairing in the normal state. We explicitly show that the fundamental constraints imposed by the Ward identities and Q-limit Ward identity are indeed satisfied.
Chang, Soon Yong
2008-04-01
In the recent years, dilute Fermi gases have played the center stage role in the many-body physics. The gas of neutral alkali atoms such as Lithium-6 and Potassium-40 can be trapped at temperatures below the Fermi degeneracy. The most relevant feature of these gases is that the interaction is tunable and strongly interacting superfluid can be artificially created. I will discuss the recent progress in understanding the ground state properties of the dilute Fermi gases at different interaction regimes. First, I will present the case of the spin symmetric systems where the Fermi gas can smoothly crossover from the BCS regime to the BEC regime. Then, I will discuss the case of the spin polarized systems, where different quantum phases can occur as a function of the polarization. In the laboratory, the trapped Fermi gas shows spatial dependence of the different quantum phases. This can be understood in the context of the local variation of the chemical potential. I will present the most accurate quantum ab initio results and the relevant experiments.
Generalized BEC and crossover theories of superconductors and ultracold Fermi gases
Energy Technology Data Exchange (ETDEWEB)
Grether, M. [Facultad de Ciencias, Universidad Nacional Autónoma de México, 04510 México DF (Mexico); Llano, M. de, E-mail: dellano@servidor.unam.mx [Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apdo. Postal 70-360, 04510 México DF (Mexico)
2013-10-15
Highlights: • A generalized BEC (GBEC) formalism of superconductivity is discussed. • GBEC includes BCS and BEC as special cases, as well as the Friedberg-T.D. Lee model. • It leads to substantial enhancements in critical superconducting temperatures. • In ultracold boson or fermion gases divergent scattering lengths are dealt with. -- Abstract: The generalized Bose–Einstein condensation (GBEC) formalism of superconductivity hinges on three separate new ingredients: (a) treatment of Cooper pairs as real bosons, (b) inclusion of two-hole pairs on an equal footing with two-electron ones, and (c) inclusion in the resulting ternary ideal boson–fermion gas of boson–fermion vertex interactions that drive formation/disin-tegration processes. Besides subsuming both BCS and BEC theories as well as the well-known crossover picture as special cases, GBEC leads to several-order-of-magnitude enhancement in the critical superconducting temperature T{sub c}. The crossover picture is applicable also to ultracold atomic clouds, both bosonic and fermionic. But low-density expansions involving the interatomic scattering length a diverge term-by-term around the so-called unitary zone about the Feshbach resonance. However, expanding a in powers of the attractive part of the interatomic potential renders smooth, divergence-free low-density expansions.
National Aeronautics and Space Administration — Fermi is a powerful space observatory that will open a wide window on the universe. Gamma rays are the highest-energy form of light, and the gamma-ray sky is...
Superfluidity and collective modes in Rashba spin–orbit coupled Fermi gases
Energy Technology Data Exchange (ETDEWEB)
He, Lianyi, E-mail: lianyi@th.physik.uni-frankfurt.de [Frankfurt Institute for Advanced Studies and Institute for Theoretical Physics, J. W. Goethe University, 60438 Frankfurt am Main (Germany); Huang, Xu-Guang, E-mail: xhuang@th.physik.uni-frankfurt.de [Center for Exploration of Energy and Matter and Physics Department, Indiana University, Bloomington, IN 47408 (United States)
2013-10-15
We present a theoretical study of the superfluidity and the corresponding collective modes in two-component atomic Fermi gases with s-wave attraction and synthetic Rashba spin–orbit coupling. The general effective action for the collective modes is derived from the functional path integral formalism. By tuning the spin–orbit coupling from weak to strong, the system undergoes a crossover from an ordinary BCS/BEC superfluid to a Bose–Einstein condensate of rashbons. We show that the properties of the superfluid density and the Anderson–Bogoliubov mode manifest this crossover. At large spin–orbit coupling, the superfluid density and the sound velocity become independent of the strength of the s-wave attraction. The two-body interaction among the rashbons is also determined. When a Zeeman field is turned on, the system undergoes quantum phase transitions to some exotic superfluid phases which are topologically nontrivial. For the two-dimensional system, the nonanalyticities of the thermodynamic functions and the sound velocity across the phase transition are related to the bulk gapless fermionic excitation which causes infrared singularities. The superfluid density and the sound velocity behave nonmonotonically: they are suppressed by the Zeeman field in the normal superfluid phase, but get enhanced in the topological superfluid phase. The three-dimensional system is also studied. -- Highlights: •The general effective action for Rashba spin–orbit coupled Fermi superfluids is derived. •The evolution of the collective modes manifests the BCS/BEC-rashbon crossover. •The superfluid properties are universal at large spin–orbit coupling. •The sound velocity behaves nonanalytically across the quantum phase transition.
Institute of Scientific and Technical Information of China (English)
Dong Hang; Ma Yong-Li
2009-01-01
Using quantum hydrodynamic approaches, we study the quantum pressure correction to the collective excitation spectrum of the interacting trapped superfluid Fermi gases in the BEC-BCS crossover. Based on a phenomenological equation of state, we derive hydrodynamic equations of the system in the whole BEC-BCS crossover regime. Beyond the Thomas-Fermi approximation, expressions of the frequency corrections of collective modes for both spherical and axial symmetric traps excited in the BEC-BCS crossover are given explicitly. The corrections of the eigenfrequencies due to the quantum pressure and their dependence on the inverse interaction strength. Anisotropic parameter and particle numbers of the condensate are discussed in detail.
Strongly correlated Bose gases
Chevy, F.; Salomon, C.
2016-10-01
The strongly interacting Bose gas is one of the most fundamental paradigms of quantum many-body physics and the subject of many experimental and theoretical investigations. We review recent progress on strongly correlated Bose gases, starting with a description of beyond mean-field corrections. We show that the Efimov effect leads to non universal phenomena and to a metastability of the low temperature Bose gas through three-body recombination to deeply bound molecular states. We outline differences and similarities with ultracold Fermi gases, discuss recent experiments on the unitary Bose gas, and finally present a few perspectives for future research.
Density-functional theory of strongly correlated Fermi gases in elongated harmonic traps
Xianlong, Gao; Polini, Marco; Asgari, Reza; Tosi, M. P.
2006-03-01
Two-component Fermi gases with tunable repulsive or attractive interactions inside quasi-one-dimensional (Q1D) harmonic wells may soon become the cleanest laboratory realizations of strongly correlated Luttiger and Luther-Emery liquids under confinement. We present a microscopic Kohn-Sham density-functional theory of these systems, with specific attention to a gas on the approach to a confinement-induced Feshbach resonance. The theory employs the one-dimensional Gaudin-Yang model as the reference system and transfers the appropriate Q1D ground-state correlations to the confined inhomogeneous gas via a suitable local-density approximation to the exchange and correlation energy functional. Quantitative understanding of the role of the interactions in the bulk shell structure of the axial density profile is thereby achieved. While repulsive intercomponent interactions depress the amplitude of the shell structure of the noninteracting gas, attractive interactions stabilize atomic-density waves through spin pairing. These should be clearly observable in atomic clouds containing of the order of up to 100 atoms.
Spin-orbit Coupled Fermi Gases and Heavy Solitons in Fermionic Superfluids
Cheuk, Lawrence
2013-05-01
The coupling of the spin of electrons to their motional state lies at the heart of topological phases of matter. We have created and detected spin-orbit coupling in an atomic Fermi gas via spin-injection spectroscopy, which characterizes the energy-momentum dispersion and spin composition of the quantum states. For energies within the spin-orbit gap, the system acts as a spin diode. To fully inhibit transport, we open an additional spin gap with radio-frequency coupling, thereby creating a spin-orbit coupled lattice whose spinful band structure we probe. In the presence of s-wave interactions, spin-orbit coupled fermion systems should display induced p-wave pairing and consequently topological superfluidity. Such systems can be described by a relativistic Dirac theory with a mass term that can be made to vary spatially. Topologically protected edge states are expected to occur whenever the mass term changes sign. A system that similarly supports edges states is the strongly interacting atomic Fermi gas near a Feshbach resonance. Topological excitations, such as vortices - line defects - or solitons - planar defects - have been described theoretically for decades in many different physical contexts. In superconductivity and superfluidity they represent a defect in the order parameter and give rise to localized bound states. We have created and directly observed solitons in a fermionic superfluid by imprinting a phase step into the superfluid wavefunction. These are found to be stable for many seconds, allowing us to track their oscillatory motion in the trapped superfluid. Their trapping period increases dramatically as the interactions are tuned from the BEC to the BCS regime. At the Feshbach resonance, their period is an order of magnitude larger than expectations from mean-field Bogoliubov-de Gennes theory, signaling strong effects of bosonic quantum fluctuations and possible filling of Andreev bound states. Our work opens the study of fermionic edge states in
Mixtures of ultracold gases: Fermi sea and Bose-Einstein condensate of lithium isotopes
Schreck, F.
2003-03-01
This thesis presents studies of quantum degenerate atomic gases of fermionic ^6Li and bosonic ^7Li. Degeneracy is reached by evaporative cooling of ^7Li in a strongly confining magnetic trap. Since at low temperatures direct evaporative cooling is not possible for a polarized fermionic gas, ^6Li is sympathetically cooled by thermal contact with ^7Li. In a first series of experiments both isotopes are trapped in their low-field seeking higher hyperfine states. A Fermi degeneracy of T/T_F=0.25(5) is achieved for 10^5 fermions. For more than 300 atoms, the ^7Li condensate collapses, due to the attractive interatomic interaction in this state. This limits the degeneracy reached for both species. To overcome this limit, in a second series of experiments ^7Li and ^6Li atoms are transferred to their low field seeking lower hyperfine states, where the boson-boson interaction is repulsive but weak. The inter-isotope collisions are used to thermalize the mixture. A ^7Li Bose-Einstein condensate (BEC) of 10^4 atoms immersed in a Fermi sea is produced. The BEC is quasi-one-dimensional and the thermal fraction can be negligible. The measured degeneracies are T/T_C=T/T_F=0.2(1). The temperature is measured using the bosonic thermal fraction, which vanishes at the lowest temperatures, limiting our measurement sensitivity. In a third series of experiments, the bosons are transferred into an optical trap and their internal state is changed to |F=1,m_F=1rangle, the lowest energy state. A Feshbach resonance is detected and used to produce a BEC with tunable atomic interactions. When the effective interaction between atoms is tuned to be small and attractive, we observe the formation of a matter-wave bright soliton. Propagation of the soliton without spreading over a macroscopic distance of 1.1 mm is observed. Mélanges de gaz ultrafroids: mer de Fermi et condensat de Bose-Einstein des isotopes du lithium Cette thèse décrit l'étude des gaz de fermions ^6Li et de bosons ^7Li dans le
2010-05-13
indicated by the solid red line, the others by dashed red lines. The “RPA Stoner” instability corresponds to the RPA result with bare as opposed to...is the scattering length and kF is the Fermi momentum. In contrast, using bare interac- tions [13] results in an unphysical divergence of the growth...the T-matrix via the Lippmann-Schwinger equation. To cor- rectly renormalize the Cooperon, we compare the Lippmann- Schwinger equations in a Fermi
In-medium bound-state formation and inhomogeneous condensation in Fermi gases in a hard-wall box
Roscher, Dietrich
2016-01-01
The formation of bosonic bound states underlies the formation of a superfluid ground state in the many-body phase diagram of ultracold Fermi gases. We study bound-state formation in a spin- and mass-imbalanced ultracold Fermi gas confined in a box with hard-wall boundary conditions. Because of the presence of finite Fermi spheres, the center-of-mass momentum of the potentially formed bound states can be finite, depending on the parameters controlling mass and spin imbalance as well as the coupling strength. We exploit this observation to estimate the potential location of inhomogeneous phases in the many-body phase diagram as a function of spin- and mass imbalance as well as the box size. Our results suggest that a hard-wall box does not alter substantially the many-body phase diagram calculated in the thermodynamic limit. Therefore, such a box may serve as an ideal trap potential to bring experiment and theory closely together and facilitate the search for exotic inhomogeneous ground states.
DEFF Research Database (Denmark)
Pekker, D; Babadi, M; Sensarma, R
2011-01-01
We study the quench dynamics of a two-component ultracold Fermi gas from the weak into the strong interaction regime, where the short time dynamics are governed by the exponential growth rate of unstable collective modes. We obtain an effective interaction that takes into account both Pauli...
Spin-orbit-coupled two-electron Fermi gases of ytterbium atoms
Song, Bo; He, Chengdong; Zhang, Shanchao; Hajiyev, Elnur; Huang, Wei; Liu, Xiong-Jun; Jo, Gyu-Boong
2016-12-01
We demonstrate all-optical implementation of spin-orbit coupling (SOC) in a two-electron Fermi gas of 173Yb atoms by coupling two hyperfine ground states with a narrow optical transition. Due to the SU (N ) symmetry of the S10 ground-state manifold which is insensitive to external magnetic fields, an optical ac Stark effect is applied to split the ground spin states, which exhibits a high stability compared with experiments on alkali-metal and lanthanide atoms, and separate out an effective spin-1/2 subspace from other hyperfine levels for the realization of SOC. The dephasing spin dynamics when a momentum-dependent spin-orbit gap is suddenly opened and the asymmetric momentum distribution of the spin-orbit-coupled Fermi gas are observed as a hallmark of SOC. The realization of all-optical SOC for ytterbium fermions should offer a route to a long-lived spin-orbit-coupled Fermi gas and greatly expand our capability of studying spin-orbit physics with alkaline-earth-metal-like atoms.
Ivanisenko, P V
2012-01-01
The Kramers problem for quantum fermi-gases with specular - diffuse boundary conditions of the kinetic theory is considered. On an example of Kramers problem the new generalised method of a source of the decision of the boundary problems from the kinetic theory is developed. The method allows to receive the decision with any degree of accuracy. At the basis of a method lays the idea of representation of a boundary condition on distribution function in the form of a source in the kinetic equation. By means of integrals Fourier the kinetic equation with a source is reduced to the integral equation of Fredholm type of the second kind. The decision is received in the form of Neumann's series.
The contact in the BCS–BEC crossover for finite range interacting ultracold Fermi gases
Energy Technology Data Exchange (ETDEWEB)
Caballero-Benítez, Santiago F., E-mail: scaballero@fisica.unam.mx; Paredes, Rosario; Romero-Rochín, Víctor
2013-10-15
Using mean-field theory for the Bardeen–Cooper–Schriefer (BCS) to the Bose–Einstein condensate (BEC) crossover we investigate the ground state thermodynamic properties of an interacting homogeneous Fermi gas. The interatomic interactions modelled through a finite range potential allows us to calculate the thermodynamic behaviour as a function of the potential parameters in the whole crossover region. We concentrate in studying the Contact variable, the thermodynamic conjugate of the inverse of the s-wave scattering length. Our analysis leads to predict a quantum phase transition – like in the case of large potential range. This finding is a direct consequence of the k-dependent energy gap.
Spin-orbit coupled two-electron Fermi gases of ytterbium atoms
Song, Bo; Zhang, Shanchao; Zou, Yueyang; Haciyev, Elnur; Huang, Wei; Liu, Xiong-Jun; Jo, Gyu-Boong
2016-01-01
We demonstrate the spin-orbit coupling (SOC) in a two-electron Fermi gas of $^{173}$Yb atoms by coupling two hyperfine ground states via the two-photon Raman transition. Due to the SU($N$) symmetry of the $^1$S$_0$ ground-state manifold which is insensitive to external magnetic field, an optical AC Stark effect is applied to split the ground spin states and separate an effective spin-1/2 subspace out from other hyperfine levels for the realization of SOC. With a momentum-dependent spin-orbit gap being suddenly opened by switching on the Raman transition, the dephasing of spin dynamics is observed, as a consequence of the momentum-dependent Rabi oscillations. Moreover, the momentum asymmetry of the spin-orbit coupled Fermi gas is also examined after projection onto the bare spin state and the corresponding momentum distribution is measured for different two-photon detuning. The realization of SOC for Yb fermions may open a new avenue to the study of novel spin-orbit physics with alkaline-earth-like atoms.
Experimental studies of spin-imbalanced Fermi gases in 2D geometries
Thomas, John
We study the thermodynamics of a quasi-two-dimensional Fermi gas, which is not quite two-dimensional (2D), but far from three dimensional (3D). This system offers opportunities to test predictions that cross interdisciplinary boundaries, such as enhanced superfluid transition temperatures in spin-imbalanced quasi-2D superconductors, and provides important benchmarks for calculations of the phase diagrams. In the experiments, an ultra-cold Fermi gas is confined in an infrared CO2 laser standing-wave, which produces periodic pancake-shaped potential wells, separated by 5.3 μm. To study the thermodynamics, we load an ultra-cold mixture of N1 = 800 spin 1/2 -up and N2 interaction strength and spin imbalance N2/N1. The measured properties are in disagreement with 2D-BCS theory, but can be fit by a 2D-polaron gas model, where each atom is surrounded by a cloud of particle-hole pairs of the opposite spin. However, this model fails to predict a transition to a spin-balanced central region as N2/N1is increased. Supported by the physics divisions of ARO, AFOSR, and NSF and by the Division of Materials Science and Engineering, the Office of Basic Energy Sciences, DOE.
Mazzucchi, Gabriel; Caballero-Benitez, Santiago F.; Mekhov, Igor B.
2016-08-01
Ultracold atomic systems offer a unique tool for understanding behavior of matter in the quantum degenerate regime, promising studies of a vast range of phenomena covering many disciplines from condensed matter to quantum information and particle physics. Coupling these systems to quantized light fields opens further possibilities of observing delicate effects typical of quantum optics in the context of strongly correlated systems. Measurement backaction is one of the most funda- mental manifestations of quantum mechanics and it is at the core of many famous quantum optics experiments. Here we show that quantum backaction of weak measurement can be used for tailoring long-range correlations of ultracold fermions, realizing quantum states with spatial modulations of the density and magnetization, thus overcoming usual requirement for a strong interatomic interactions. We propose detection schemes for implementing antiferromagnetic states and density waves. We demonstrate that such long-range correlations cannot be realized with local addressing, and they are a consequence of the competition between global but spatially structured backaction of weak quantum measurement and unitary dynamics of fermions.
Mazzucchi, Gabriel; Caballero-Benitez, Santiago F; Mekhov, Igor B
2016-08-11
Ultracold atomic systems offer a unique tool for understanding behavior of matter in the quantum degenerate regime, promising studies of a vast range of phenomena covering many disciplines from condensed matter to quantum information and particle physics. Coupling these systems to quantized light fields opens further possibilities of observing delicate effects typical of quantum optics in the context of strongly correlated systems. Measurement backaction is one of the most funda- mental manifestations of quantum mechanics and it is at the core of many famous quantum optics experiments. Here we show that quantum backaction of weak measurement can be used for tailoring long-range correlations of ultracold fermions, realizing quantum states with spatial modulations of the density and magnetization, thus overcoming usual requirement for a strong interatomic interactions. We propose detection schemes for implementing antiferromagnetic states and density waves. We demonstrate that such long-range correlations cannot be realized with local addressing, and they are a consequence of the competition between global but spatially structured backaction of weak quantum measurement and unitary dynamics of fermions.
Verification of an analytic fit for the vortex core profile in superfluid Fermi gases
Energy Technology Data Exchange (ETDEWEB)
Verhelst, Nick, E-mail: nick.verhelst@uantwerpen.be [TQC, Universiteit Antwerpen, Universiteitsplein 1, B-2610 Antwerpen (Belgium); Klimin, Serghei, E-mail: sergei.klimin@uantwerpen.be [TQC, Universiteit Antwerpen, Universiteitsplein 1, B-2610 Antwerpen (Belgium); Department of Theoretical Physics, State University of Moldova, Republic of Moldova (Moldova, Republic of); Tempere, Jacques [TQC, Universiteit Antwerpen, Universiteitsplein 1, B-2610 Antwerpen (Belgium); Lyman Laboratory of Physics, Harvard University (United States)
2017-02-15
Highlights: • The vortex profile in an imbalanced Fermi condensate is investigated. • The analytic fit for the vortex profile is compared with numerical simulations. • The analytic fit excellently agrees with numeric results in the BCS-BEC crossover. - Abstract: A characteristic property of superfluidity and -conductivity is the presence of quantized vortices in rotating systems. To study the BEC-BCS crossover the two most common methods are the Bogoliubov-De Gennes theory and the usage of an effective field theory. In order to simplify the calculations for one vortex, it is often assumed that the hyperbolic tangent yields a good approximation for the vortex structure. The combination of a variational vortex structure, together with cylindrical symmetry yields analytic (or numerically simple) expressions. The focus of this article is to investigate to what extent this analytic fit truly reflects the vortex structure throughout the BEC-BCS crossover at finite temperatures. The vortex structure will be determined using the effective field theory presented in [Eur. Phys. Journal B 88, 122 (2015)] and compared to the variational analytic solution. By doing this it is possible to see where these two structures agree, and where they differ. This comparison results in a range of applicability where the hyperbolic tangent will be a good fit for the vortex structure.
Probing superfluid properties in strongly correlated Fermi gases with high spatial resolution
Energy Technology Data Exchange (ETDEWEB)
Weimer, Wolf
2014-07-01
In this thesis an apparatus to study ultracold fermionic {sup 6}Li with tunable interaction strength and dimensionality is presented. The apparatus is applied to investigate the speed of sound v{sub s} and the superfluid critical velocity v{sub c} across the transition from Bose-Einstein condensation (BEC) to Bardeen-Cooper-Schrieffer (BCS) superfluidity. The results set benchmarks for theories describing strongly correlated systems. To measure v{sub c}, an obstacle, that is formed by a tightly focused laser beam, is moved through a superfluid sample with a constant velocity along a line of constant density. For velocities larger than v{sub c} heating of the gas is observed. The critical velocity is mapped out for various different interaction strengths covering the BEC-BCS crossover. According to the Landau criterion and Bogolyubov theory, v{sub c} should be closely related to v{sub s} in a Bose-Einstein condensate. The measurement of v{sub s} is conducted by creating a density modulation in the centre of the cloud and tracking the excited modulation. The velocities v{sub s} and v{sub c} are measured in a similar range of interaction strengths and in similar samples to ensure comparability. The apparatus which provides the ultracold samples is a two chamber design with a magneto-optical trap that is loaded via a Zeeman slower. The subsequent cooling steps are all-optical and finally create an ultracold oblate atom cloud inside a flat vacuum cell. This cell provides optimal optical access and is placed between two high numerical aperture microscope objectives. These objectives are used to probe the samples in-situ on length scales which are comparable to the intrinsic length scales of the gases. Similarly, optical dipole potentials are employed to manipulate the clouds on the same small length scales. The oblate samples are sufficiently flat such that there spatial extent along the microscope axes is smaller than the depth of field of the objectives. With an
Exploring the thermodynamics of a universal Fermi gas.
Nascimbène, S; Navon, N; Jiang, K J; Chevy, F; Salomon, C
2010-02-25
One of the greatest challenges in modern physics is to understand the behaviour of an ensemble of strongly interacting particles. A class of quantum many-body systems (such as neutron star matter and cold Fermi gases) share the same universal thermodynamic properties when interactions reach the maximum effective value allowed by quantum mechanics, the so-called unitary limit. This makes it possible in principle to simulate some astrophysical phenomena inside the highly controlled environment of an atomic physics laboratory. Previous work on the thermodynamics of a two-component Fermi gas led to thermodynamic quantities averaged over the trap, making comparisons with many-body theories developed for uniform gases difficult. Here we develop a general experimental method that yields the equation of state of a uniform gas, as well as enabling a detailed comparison with existing theories. The precision of our equation of state leads to new physical insights into the unitary gas. For the unpolarized gas, we show that the low-temperature thermodynamics of the strongly interacting normal phase is well described by Fermi liquid theory, and we localize the superfluid transition. For a spin-polarized system, our equation of state at zero temperature has a 2 per cent accuracy and extends work on the phase diagram to a new regime of precision. We show in particular that, despite strong interactions, the normal phase behaves as a mixture of two ideal gases: a Fermi gas of bare majority atoms and a non-interacting gas of dressed quasi-particles, the fermionic polarons.
Yu, Yi-Cong; Guan, Xi-Wen
2017-06-01
We present a unified derivation of the pressure equation of states, thermodynamics and scaling functions for the one-dimensional (1D) strongly attractive Fermi gases with SU(w) symmetry. These physical quantities provide a rigorous understanding on a universality class of quantum criticality characterized by the critical exponents z = 2 and correlation length exponent ν = 1/2. Such a universality class of quantum criticality can occur when the Fermi sea of one branch of charge bound states starts to fill or becomes gapped at zero temperature. The quantum critical cone can be determined by the double peaks in specific heat, which serve to mark two crossover temperatures fanning out from the critical point. Our method opens to further study on quantum phases and phase transitions in strongly interacting fermions with large SU(w) and non-SU(w) symmetries in one dimension. Supported by the National Natural Science Foundation of China under Grant No 11374331 and the key NSFC under Grant No 11534014. XWG has been partially supported by the Australian Research Council.
Directory of Open Access Journals (Sweden)
Antonello Sindona
2015-03-01
Full Text Available The sudden introduction of a local impurity in a Fermi sea leads to an anomalous disturbance of its quantum state that represents a local quench, leaving the system out of equilibrium and giving rise to the Anderson orthogonality catastrophe. The statistics of the work done describe the energy fluctuations produced by the quench, providing an accurate and detailed insight into the fundamental physics of the process. We present here a numerical approach to the non-equilibrium work distribution, supported by applications to phenomena occurring at very diverse energy ranges. One of them is the valence electron shake-up induced by photo-ionization of a core state in a fullerene molecule. The other is the response of an ultra-cold gas of trapped fermions to an embedded two-level atom excited by a fast pulse. Working at low thermal energies, we detect the primary role played by many-particle states of the perturbed system with one or two excited fermions. We validate our approach through the comparison with some photoemission data on fullerene films and previous analytical calculations on harmonically trapped Fermi gases.
Sindona, Antonello; Pisarra, Michele; Gravina, Mario; Vacacela Gomez, Cristian; Riccardi, Pierfrancesco; Falcone, Giovanni; Plastina, Francesco
2015-01-01
The sudden introduction of a local impurity in a Fermi sea leads to an anomalous disturbance of its quantum state that represents a local quench, leaving the system out of equilibrium and giving rise to the Anderson orthogonality catastrophe. The statistics of the work done describe the energy fluctuations produced by the quench, providing an accurate and detailed insight into the fundamental physics of the process. We present here a numerical approach to the non-equilibrium work distribution, supported by applications to phenomena occurring at very diverse energy ranges. One of them is the valence electron shake-up induced by photo-ionization of a core state in a fullerene molecule. The other is the response of an ultra-cold gas of trapped fermions to an embedded two-level atom excited by a fast pulse. Working at low thermal energies, we detect the primary role played by many-particle states of the perturbed system with one or two excited fermions. We validate our approach through the comparison with some photoemission data on fullerene films and previous analytical calculations on harmonically trapped Fermi gases.
Hydrodynamics of a unitary Bose gas
Man, Jay; Fletcher, Richard; Lopes, Raphael; Navon, Nir; Smith, Rob; Hadzibabic, Zoran
2016-05-01
In general, normal-phase Bose gases are well described by modelling them as ideal gases. In particular, hydrodynamic flow is usually not observed in the expansion dynamics of normal gases, and is more readily observable in Bose-condensed gases. However, by preparing strongly-interacting clouds, we observe hydrodynamic behaviour in normal-phase Bose gases, including the `maximally' hydrodynamic unitary regime. We avoid the atom losses that often hamper experimental access of this regime by using radio-frequency injection, which switches on interactions much faster than trap or loss timescales. At low phase-space densities, we find excellent agreement with a collisional model based on the Boltzmann equation. At higher phase-space densities our results show a deviation from this model in the vicinity of an Efimov resonance, which cannot be accounted for by measured losses.
Unitary lens semiconductor device
Lear, Kevin L.
1997-01-01
A unitary lens semiconductor device and method. The unitary lens semiconductor device is provided with at least one semiconductor layer having a composition varying in the growth direction for unitarily forming one or more lenses in the semiconductor layer. Unitary lens semiconductor devices may be formed as light-processing devices such as microlenses, and as light-active devices such as light-emitting diodes, photodetectors, resonant-cavity light-emitting diodes, vertical-cavity surface-emitting lasers, and resonant cavity photodetectors.
Phase Diagram of a Strongly Interacting Spin-Imbalanced Fermi Gas
Olsen, Ben A; Fry, Jacob A; Sheehy, Daniel E; Hulet, Randall G
2015-01-01
We obtain the phase diagram of spin-imbalanced interacting Fermi gases from measurements of density profiles of $^6$Li atoms in a harmonic trap. These results agree with, and extend, previous experimental measurements. Measurements of the critical polarization at which the balanced superfluid core vanishes generally agree with previous experimental results and with quantum Monte Carlo (QMC) calculations in the BCS and unitary regimes. We disagree with the QMC results in the BEC regime, however, where the measured critical polarizations are greater than theoretically predicted. We also measure the equation of state in the crossover regime for a gas with equal numbers of the two fermion spin states.
Cowling, W R
2001-06-01
Unitary appreciative inquiry is described as an orientation, process, and approach for illuminating the wholeness, uniqueness, and essence that are the pattern of human life. It was designed to bring the concepts, assumptions, and perspectives of the science of unitary human beings into reality as a mode of inquiry. Unitary appreciative inquiry provides a way of giving fullest attention to important facets of human life that often are not fully accounted for in current methods that have a heavier emphasis on diagnostic representations. The participatory, synoptic, and transformative qualities of the unitary appreciative process are explicated. The critical dimensions of nursing knowledge development expressed in dialectics of the general and the particular, action and theory, stories and numbers, sense and soul, aesthetics and empirics, and interpretation and emancipation are considered in the context of the unitary appreciative stance. Issues of legitimacy of knowledge and credibility of research are posed and examined in the context of four quality standards that are deemed important to evaluate the worthiness of unitary appreciative inquiry for the advancement of nursing science and practice.
2016-02-02
frequencies ) are smaller than the spontaneous emission rate ge. Unfortunately, this method is invalid in the bare basis for broad resonances, where the...classification in accordance with security classification regulations , e.g. U, C, S, etc. If this form contains classified information, stamp classification...show that the EIT method creates narrow features in the scattering phase shift, enabling control by optical frequency rather than intensity, providing
Entanglement quantification by local unitaries
Monras, A; Giampaolo, S M; Gualdi, G; Davies, G B; Illuminati, F
2011-01-01
Invariance under local unitary operations is a fundamental property that must be obeyed by every proper measure of quantum entanglement. However, this is not the only aspect of entanglement theory where local unitaries play a relevant role. In the present work we show that the application of suitable local unitary operations defines a family of bipartite entanglement monotones, collectively referred to as "shield entanglement". They are constructed by first considering the (squared) Hilbert- Schmidt distance of the state from the set of states obtained by applying to it a given local unitary. To the action of each different local unitary there corresponds a different distance. We then minimize these distances over the sets of local unitaries with different spectra, obtaining an entire family of different entanglement monotones. We show that these shield entanglement monotones are organized in a hierarchical structure, and we establish the conditions that need to be imposed on the spectrum of a local unitary f...
Lacroix, Denis; Boulet, Antoine; Grasso, Marcella; Yang, C.-J.
2017-05-01
We further progress along the line of Ref. [D. Lacroix, Phys. Rev. A 94, 043614 (2016), 10.1103/PhysRevA.94.043614] where a functional for Fermi systems with anomalously large s -wave scattering length as was proposed that has no free parameters. The functional is designed to correctly reproduce the unitary limit in Fermi gases together with the leading-order contributions in the s - and p -wave channels at low density. The functional is shown to be predictive up to densities ˜0.01 fm-3 that is much higher densities compared to the Lee-Yang functional, valid for ρ bare interaction are strongly renormalized by medium effects. As a consequence, some of the scales at play around saturation are dominated by the unitary gas properties and not directly by low-energy constants. For instance, we show that the scale in the s -wave channel around saturation is proportional to the so-called Bertsch parameter ξ0 and becomes independent of as. We also point out that these scales are of the same order of magnitude than those empirically obtained in the Skyrme energy density functional. We finally propose a slight modification of the functional such that it becomes accurate up to the saturation density ρ ≃0.16 fm-3.
Energy Technology Data Exchange (ETDEWEB)
Yan, D; Kevrekidis, P G [Department of Mathematics and Statistics, University of Massachusetts, Amherst, MA 01003-4515 (United States); Frantzeskakis, D J, E-mail: kevrekid@math.umass.edu [Department of Physics, University of Athens, Panepistimiopolis, Zografos, Athens 157 84 (Greece)
2011-10-14
In this work, we consider a model of a defocusing nonlinear Schroedinger equation with a variable nonlinearity exponent. This is motivated by the study of a superfluid Fermi gas in the Bose-Einstein condensation (BEC)-Bardeen-Cooper-Schrieffer crossover. In particular, we focus on the relevant mean-field model in the regime from BEC to unitarity and especially consider the modification of the nearly black soliton oscillation frequency due to the variation in the nonlinearity exponent in a harmonic trapping potential. The analytical expressions given as a function of the relevant nonlinearity exponent are corroborated by numerical computations and also extended past the BEC limit. (paper)
Entanglement Continuous Unitary Transformations
Sahin, S; Orus, R
2016-01-01
Continuous unitary transformations are a powerful tool to extract valuable information out of quantum many-body Hamiltonians, in which the so-called flow equation transforms the Hamiltonian to a diagonal or block-diagonal form in second quantization. Yet, one of their main challenges is how to approximate the infinitely-many coupled differential equations that are produced throughout this flow. Here we show that tensor networks offer a natural and non-perturbative truncation scheme in terms of entanglement. The corresponding scheme is called "entanglement-CUT" or eCUT. It can be used to extract the low-energy physics of quantum many-body Hamiltonians, including quasiparticle energy gaps. We provide the general idea behind eCUT and explain its implementation for finite 1d systems using the formalism of matrix product operators, and we present proof-of-principle results for the spin-1/2 1d quantum Ising model in a transverse field. Entanglement-CUTs can also be generalized to higher dimensions and to the thermo...
Entanglement continuous unitary transformations
Sahin, Serkan; Schmidt, Kai Phillip; Orús, Román
2017-01-01
Continuous unitary transformations are a powerful tool to extract valuable information out of quantum many-body Hamiltonians, in which the so-called flow equation transforms the Hamiltonian to a diagonal or block-diagonal form in second quantization. Yet, one of their main challenges is how to approximate the infinitely-many coupled differential equations that are produced throughout this flow. Here we show that tensor networks offer a natural and non-perturbative truncation scheme in terms of entanglement. The corresponding scheme is called “entanglement-CUT” or eCUT. It can be used to extract the low-energy physics of quantum many-body Hamiltonians, including quasiparticle energy gaps. We provide the general idea behind eCUT and explain its implementation for finite 1d systems using the formalism of matrix product operators. We also present proof-of-principle results for the spin-(1/2) 1d quantum Ising model and the 3-state quantum Potts model in a transverse field. Entanglement-CUTs can also be generalized to higher dimensions and to the thermodynamic limit.
Unitary Transformation in Quantum Teleportation
Institute of Scientific and Technical Information of China (English)
WANG Zheng-Chuan
2006-01-01
In the well-known treatment of quantum teleportation, the receiver should convert the state of his EPR particle into the replica of the unknown quantum state by one of four possible unitary transformations. However, the importance of these unitary transformations must be emphasized. We will show in this paper that the receiver cannot transform the state of his particle into an exact replica of the unknown state which the sender wants to transfer if he has not a proper implementation of these unitary transformations. In the procedure of converting state, the inevitable coupling between EPR particle and environment which is needed by the implementation of unitary transformations will reduce the accuracy of the replica.
All maximally entangling unitary operators
Energy Technology Data Exchange (ETDEWEB)
Cohen, Scott M. [Department of Physics, Duquesne University, Pittsburgh, Pennsylvania 15282 (United States); Department of Physics, Carnegie-Mellon University, Pittsburgh, Pennsylvania 15213 (United States)
2011-11-15
We characterize all maximally entangling bipartite unitary operators, acting on systems A and B of arbitrary finite dimensions d{sub A}{<=}d{sub B}, when ancillary systems are available to both parties. Several useful and interesting consequences of this characterization are discussed, including an understanding of why the entangling and disentangling capacities of a given (maximally entangling) unitary can differ and a proof that these capacities must be equal when d{sub A}=d{sub B}.
Institute of Scientific and Technical Information of China (English)
王俊; 高先龙
2015-01-01
It was investigated the properties of spin-orbit coupled atomic fermi gases under a Zeeman field. By solving the Bogoliubove-de Gennes equation self-consistently, it was found that the system supported the topol-ogical superfluid state and the Fulde-Ferrell-Larkin-Ovchinnikov superfluid state respectively when the system under the different strength of Zeeman field and filling factors. When the system turned into topological super-fluid state, a pair of zero-energy Majorana fermions were found.%研究了具有自旋轨道耦合的冷原子费米气在外磁场作用下的物理性质。通过自洽求解Bogoliubove-de Gennes方程，发现了在不同磁场强度和粒子填充数下，体系分别存在拓扑超流态和 Fulde-Ferrell-Larkin-Ovchinnikov超流态。当体系处于拓扑超流态时，存在零能Majorana费米子。
Strongly interacting ultracold quantum gases
Institute of Scientific and Technical Information of China (English)
Hui ZHAI
2009-01-01
This article reviews recent progresses in ul- tracold quantum gases, and it includes three subjects which are the Fermi gases across a Feshbach resonance, quantum gases in the optical lattices and the fast ro- tating quantum gases. In this article, we discuss many basic physics pictures and concepts in quantum gases, for examples, the resonant interaction, universality and condensation in the lowest Landau level; we introduce fundamental theoretical tools for studying these systems, such as mean-field theory for BEC-BCS crossover and for the boson Hubbard model; also, we emphasize the im- portant unsolved problems in the forefront of this field, for instance, the temperature effect in optical lattices.
Unitary pattern: a review of theoretical literature.
Musker, Kathleen M
2012-07-01
It is the purpose of this article to illuminate the phenomenon of unitary pattern through a review of theoretical literature. Unitary pattern is a phenomenon of significance to the discipline of nursing because it is manifested in and informs all person-environment health experiences. Unitary pattern was illuminated by: addressing the barriers to understanding the phenomenon, presenting a definition of unitary pattern, and exploring Eastern and Western theoretical literature which address unitary pattern in a way that is congruent with the definition presented. This illumination of unitary pattern will expand nursing knowledge and contribute to the discipline of nursing.
Despair: a unitary appreciative inquiry.
Cowling, W Richard
2004-01-01
A unitary appreciative case study method was used to explicate unitary understandings of despair embedded in the unique personal life contexts of the participants. Fourteen women engaged in dialogical, appreciative interviews that led to the creation of profiles of the life pattern or course associated with despair for each woman. Three exemplar cases are detailed including the profiles that incorporate story, metaphor, music, and imagery. The voices of the women provide morphogenic knowledge of the contexts, nature, consequences, and contributions of despair as well as practical guidance for healthcare providers.
Universal Loss Dynamics in a Unitary Bose Gas
Eismann, Ulrich; Khaykovich, Lev; Laurent, Sébastien; Ferrier-Barbut, Igor; Rem, Benno S.; Grier, Andrew T.; Delehaye, Marion; Chevy, Frédéric; Salomon, Christophe; Ha, Li-Chung; Chin, Cheng
2016-04-01
The low-temperature unitary Bose gas is a fundamental paradigm in few-body and many-body physics, attracting wide theoretical and experimental interest. Here, we present experiments performed with unitary 133Cs and 7Li atoms in two different setups, which enable quantitative comparison of the three-body recombination rate in the low-temperature domain. We develop a theoretical model that describes the dynamic competition between two-body evaporation and three-body recombination in a harmonically trapped unitary atomic gas above the condensation temperature. We identify a universal "magic" trap depth where, within some parameter range, evaporative cooling is balanced by recombination heating and the gas temperature stays constant. Our model is developed for the usual three-dimensional evaporation regime as well as the two-dimensional evaporation case, and it fully supports our experimental findings. Combined 133Cs and 7Li experimental data allow investigations of loss dynamics over 2 orders of magnitude in temperature and 4 orders of magnitude in three-body loss rate. We confirm the 1 /T2 temperature universality law. In particular, we measure, for the first time, the Efimov inelasticity parameter η*=0.098 (7 ) for the 47.8-G d -wave Feshbach resonance in 133Cs. Our result supports the universal loss dynamics of trapped unitary Bose gases up to a single parameter η*.
Teleportation of M-Qubit Unitary Operations
Institute of Scientific and Technical Information of China (English)
郑亦庄; 顾永建; 郭光灿
2002-01-01
We discuss teleportation of unitary operations on a two-qubit in detail, then generalize the bidirectional state teleportation scheme from one-qubit to M-qubit unitary operations. The resources required for the optimal implementation of teleportation of an M-qubit unitary operation using a bidirectional state teleportation scheme are given.
Unitary Superfluidity Of Polarized Fermionic Gases In Highly Elongated Traps
Baksmaty, L.; Lu, H.; Bolech, C.; Pu, H.
2010-03-01
Recent groundbreaking experiments on resonantly interacting fermionic superfluids encountered qualitative and quantitative discrepancies which seem to be a function of the confining geometry. Despite long familiarity with BCS (Bardeen-Cooper-Schrieffer) superfluids in a wide range of physical systems such as nuclear matter, QCD, Astrophysics and Condensed Matter, these observations have defied theoretical explanation. Mindful of quantum rigidity and motivated by this impasse, we study the solution space for 3-dimensional fully self-consistent mean field formulation. Relying on numerical algorithms specifically developed for this purpose, we study realistic systems with up to 10^5 atoms. We find that for a large enough sample in a cigar-shaped trap, there are typically three types of solutions which are almost degenerate and have the ff. properties: (i) There is a solution very similar to the local density approximation (LDA) which is consistently the lowest in energy. (ii) However one of the other two solutions, connected by a smooth transition, and which are more consistent with experiment at high aspect ratio, supports a state very similar to the long sought FFLO (Fulde Ferrel Larkin Ovchinnikov) state. We submit that these solutions are relevant false vacua because, given high energy barriers and near degeneracy of the obtained solutions, the actual states observed in an experiment could be a strong function of the experimental procedure. Darpa OLE grant, ARO Grant no. W911NF-07-1-0464, Welch foundation (C-1669, C-1681) and NSF.
Unitary equivalence of quantum walks
Energy Technology Data Exchange (ETDEWEB)
Goyal, Sandeep K., E-mail: sandeep.goyal@ucalgary.ca [School of Chemistry and Physics, University of KwaZulu-Natal, Private Bag X54001, 4000 Durban (South Africa); Konrad, Thomas [School of Chemistry and Physics, University of KwaZulu-Natal, Private Bag X54001, 4000 Durban (South Africa); National Institute for Theoretical Physics (NITheP), KwaZulu-Natal (South Africa); Diósi, Lajos [Wigner Research Centre for Physics, Institute for Particle and Nuclear Physics, H-1525 Budapest 114, P.O.B. 49 (Hungary)
2015-01-23
Highlights: • We have found unitary equivalent classes in coined quantum walks. • A single parameter family of coin operators is sufficient to realize all simple one-dimensional quantum walks. • Electric quantum walks are unitarily equivalent to time dependent quantum walks. - Abstract: A simple coined quantum walk in one dimension can be characterized by a SU(2) operator with three parameters which represents the coin toss. However, different such coin toss operators lead to equivalent dynamics of the quantum walker. In this manuscript we present the unitary equivalence classes of quantum walks and show that all the nonequivalent quantum walks can be distinguished by a single parameter. Moreover, we argue that the electric quantum walks are equivalent to quantum walks with time dependent coin toss operator.
Institute of Scientific and Technical Information of China (English)
李琳
2006-01-01
Enrico Fermi was born in Rome on 29th September, 1901. He attended a local grammar school, and in 1918, he won a fellowship of the Scuola Normale Superiore of Pisa, where he gained his doctor’s degree in physics in 1922, with Professor Puccianti. In 1923, he was awarded a scholarship from the Italian Government. With a Rockefeller Fellowship, in 1924, he moved to Leyden, and later that same year he returned to Italy to occupy for two
Truncations of random unitary matrices
Zyczkowski, K; Zyczkowski, Karol; Sommers, Hans-Juergen
1999-01-01
We analyze properties of non-hermitian matrices of size M constructed as square submatrices of unitary (orthogonal) random matrices of size N>M, distributed according to the Haar measure. In this way we define ensembles of random matrices and study the statistical properties of the spectrum located inside the unit circle. In the limit of large matrices, this ensemble is characterized by the ratio M/N. For the truncated CUE we derive analytically the joint density of eigenvalues from which easily all correlation functions are obtained. For N-M fixed and N--> infinity the universal resonance-width distribution with N-M open channels is recovered.
Direct dialling of Haar random unitary matrices
Russell, Nicholas J.; Chakhmakhchyan, Levon; O’Brien, Jeremy L.; Laing, Anthony
2017-03-01
Random unitary matrices find a number of applications in quantum information science, and are central to the recently defined boson sampling algorithm for photons in linear optics. We describe an operationally simple method to directly implement Haar random unitary matrices in optical circuits, with no requirement for prior or explicit matrix calculations. Our physically motivated and compact representation directly maps independent probability density functions for parameters in Haar random unitary matrices, to optical circuit components. We go on to extend the results to the case of random unitaries for qubits.
Singular Value Decomposition for Unitary Symmetric Matrix
Institute of Scientific and Technical Information of China (English)
ZOUHongxing; WANGDianjun; DAIQionghai; LIYanda
2003-01-01
A special architecture called unitary sym-metric matrix which embodies orthogonal, Givens, House-holder, permutation, and row (or column) symmetric ma-trices as its special cases, is proposed, and a precise corre-spondence of singular values and singular vectors between the unitary symmetric matrix and its mother matrix is de-rived. As an illustration of potential, it is shown that, for a class of unitary symmetric matrices, the singular value decomposition (SVD) using the mother matrix rather than the unitary symmetric matrix per se can save dramatically the CPU time and memory without loss of any numerical precision.
Unitary Root Music and Unitary Music with Real-Valued Rank Revealing Triangular Factorization
2010-06-01
AFRL-RY-WP-TP-2010-1213 UNITARY ROOT MUSIC AND UNITARY MUSIC WITH REAL-VALUED RANK REVEALING TRIANGULAR FACTORIZATION (Postprint) Nizar...DATES COVERED (From - To) June 2010 Journal Article Postprint 08 September 2006 – 31 August 2009 4. TITLE AND SUBTITLE UNITARY ROOT MUSIC AND...UNITARY MUSIC WITH REAL-VALUED RANK REVEALING TRIANGULAR FACTORIZATION (Postprint) 5a. CONTRACT NUMBER 5b. GRANT NUMBER FA8650-05-D-1912-0007 5c
Relativistic Quantum Thermodynamics of Ideal Gases in 2 Dimensions
Blas, H.; Pimentel, B. M.; Tomazelli, J. L.
1999-01-01
In this work we study the behavior of relativistic ideal Bose and Fermi gases in two space dimensions. Making use of polylogarithm functions we derive a closed and unified expression for their densities. It is shown that both type of gases are essentially inequivalent, and only in the non-relativistic limit the spinless and equal mass Bose and Fermi gases are equivalent as known in the literature.
Relativistic quantum thermodynamics of ideal gases in two dimensions.
Blas, H; Pimentel, B M; Tomazelli, J L
1999-11-01
In this work we study the behavior of relativistic ideal Bose and Fermi gases in two space dimensions. Making use of polylogarithm functions we derive a closed and unified expression for their densities. It is shown that both type of gases are essentially inequivalent, and only in the non-relativistic limit the spinless and equal mass Bose and Fermi gases are equivalent as known in the literature.
Unitary symmetry, combinatorics, and special functions
Energy Technology Data Exchange (ETDEWEB)
Louck, J.D.
1996-12-31
From 1967 to 1994, Larry Biedenham and I collaborated on 35 papers on various aspects of the general unitary group, especially its unitary irreducible representations and Wigner-Clebsch-Gordan coefficients. In our studies to unveil comprehensible structures in this subject, we discovered several nice results in special functions and combinatorics. The more important of these will be presented and their present status reviewed.
Spectral stability of unitary network models
Asch, Joachim; Bourget, Olivier; Joye, Alain
2015-08-01
We review various unitary network models used in quantum computing, spectral analysis or condensed matter physics and establish relationships between them. We show that symmetric one-dimensional quantum walks are universal, as are CMV matrices. We prove spectral stability and propagation properties for general asymptotically uniform models by means of unitary Mourre theory.
Complex positive maps and quaternionic unitary evolution
Energy Technology Data Exchange (ETDEWEB)
Asorey, M [Departamento de Fisica Teorica, Universidad de Zaragoza, 50009 Zaragoza (Spain); Scolarici, G [Dipartimento di Fisica dell' Universita di Lecce and INFN, Sezione di Lecce, I-73100 Lecce (Italy)
2006-08-04
The complex projection of any n-dimensional quaternionic unitary dynamics defines a one-parameter positive semigroup dynamics. We show that the converse is also true, i.e. that any one-parameter positive semigroup dynamics of complex density matrices with maximal rank can be obtained as the complex projection of suitable quaternionic unitary dynamics.
Composed ensembles of random unitary ensembles
Pozniak, M; Kus, M; Pozniak, Marcin; Zyczkowski, Karol; Kus, Marek
1997-01-01
Composed ensembles of random unitary matrices are defined via products of matrices, each pertaining to a given canonical circular ensemble of Dyson. We investigate statistical properties of spectra of some composed ensembles and demonstrate their physical relevance. We discuss also the methods of generating random matrices distributed according to invariant Haar measure on the orthogonal and unitary group.
Tensor Products of Random Unitary Matrices
Tkocz, Tomasz; Kus, Marek; Zeitouni, Ofer; Zyczkowski, Karol
2012-01-01
Tensor products of M random unitary matrices of size N from the circular unitary ensemble are investigated. We show that the spectral statistics of the tensor product of random matrices becomes Poissonian if M=2, N become large or M become large and N=2.
Energy Transfer Using Unitary Transformations
Directory of Open Access Journals (Sweden)
Winny O'Kelly de Galway
2013-11-01
Full Text Available We study the unitary time evolution of a simple quantum Hamiltonian describing two harmonic oscillators coupled via a three-level system. The latter acts as an engine transferring energy from one oscillator to the other and is driven in a cyclic manner by time-dependent external fields. The S-matrix (scattering matrix of the cycle is obtained in analytic form. The total number of quanta contained in the system is a conserved quantity. As a consequence, the spectrum of the S-matrix is purely discrete, and the evolution of the system is quasi-periodic. The explicit knowledge of the S-matrix makes it possible to do accurate numerical evaluations of the time-dependent wave function. They confirm the quasi-periodic behavior. In particular, the energy flows back and forth between the two oscillators in a quasi-periodic manner.
Thermodynamics of Quantum Gases for the Entire Range of Temperature
Biswas, Shyamal; Jana, Debnarayan
2012-01-01
We have analytically explored the thermodynamics of free Bose and Fermi gases for the entire range of temperature, and have extended the same for harmonically trapped cases. We have obtained approximate chemical potentials for the quantum gases in closed forms of temperature so that the thermodynamic properties of the quantum gases become…
Extremal spacings of random unitary matrices
Smaczynski, Marek; Kus, Marek; Zyczkowski, Karol
2012-01-01
Extremal spacings between unimodular eigenvalues of random unitary matrices of size N pertaining to circular ensembles are investigated. Probability distributions for the minimal spacing for various ensembles are derived for N=4. We show that for large matrices the average minimal spacing s_min of a random unitary matrix behaves as N^(-1/(1+B)) for B equal to 0,1 and 2 for circular Poisson, orthogonal and unitary ensembles, respectively. For these ensembles also asymptotic probability distributions P(s_min) are obtained and the statistics of the largest spacing s_max are investigated.
Intercept Capacity: Unknown Unitary Transformation
Directory of Open Access Journals (Sweden)
Bill Moran
2008-11-01
Full Text Available We consider the problem of intercepting communications signals between Multiple-Input Multiple-Output (MIMO communication systems. To correctly detect a transmitted message it is necessary to know the gain matrix that represents the channel between the transmitter and the receiver. However, even if the receiver has knowledge of the message symbol set, it may not be possible to estimate the channel matrix. Blind Source Separation (BSS techniques, such as Independent Component Analysis (ICA can go some way to extracting independent signals from individual transmission antennae but these may have been preprocessed in a manner unknown to the receiver. In this paper we consider the situation where a communications interception system has prior knowledge of the message symbol set, the channel matrix between the transmission system and the interception system and is able to resolve the transmissionss from independent antennae. The question then becomes: what is the mutual information available to the interceptor when an unknown unitary transformation matrix is employed by the transmitter.
Unitary Approximations in Fault Detection Filter Design
Directory of Open Access Journals (Sweden)
Dušan Krokavec
2016-01-01
Full Text Available The paper is concerned with the fault detection filter design requirements that relax the existing conditions reported in the previous literature by adapting the unitary system principle in approximation of fault detection filter transfer function matrix for continuous-time linear MIMO systems. Conditions for the existence of a unitary construction are presented under which the fault detection filter with a unitary transfer function can be designed to provide high residual signals sensitivity with respect to faults. Otherwise, reflecting the emplacement of singular values in unitary construction principle, an associated structure of linear matrix inequalities with built-in constraints is outlined to design the fault detection filter only with a Hurwitz transfer function. All proposed design conditions are verified by the numerical illustrative examples.
Quantum unitary dynamics in cosmological spacetimes
Energy Technology Data Exchange (ETDEWEB)
Cortez, Jerónimo, E-mail: jacq@ciencias.unam.mx [Departamento de Física, Facultad de Ciencias, Universidad Nacional Autónoma de México, México D.F. 04510 (Mexico); Mena Marugán, Guillermo A., E-mail: mena@iem.cfmac.csic.es [Instituto de Estructura de la Materia, IEM-CSIC, Serrano 121, 28006 Madrid (Spain); Velhinho, José M., E-mail: jvelhi@ubi.pt [Departamento de Física, Faculdade de Ciências, Universidade da Beira Interior, R. Marquês D’Ávila e Bolama, 6201-001 Covilhã (Portugal)
2015-12-15
We address the question of unitary implementation of the dynamics for scalar fields in cosmological scenarios. Together with invariance under spatial isometries, the requirement of a unitary evolution singles out a rescaling of the scalar field and a unitary equivalence class of Fock representations for the associated canonical commutation relations. Moreover, this criterion provides as well a privileged quantization for the unscaled field, even though the associated dynamics is not unitarily implementable in that case. We discuss the relation between the initial data that determine the Fock representations in the rescaled and unscaled descriptions, and clarify that the S-matrix is well defined in both cases. In our discussion, we also comment on a recently proposed generalized notion of unitary implementation of the dynamics, making clear the difference with the standard unitarity criterion and showing that the two approaches are not equivalent.
Asymptotic Evolution of Random Unitary Operations
Novotny, J; Jex, I
2009-01-01
We analyze the asymptotic dynamics of quantum systems resulting from large numbers of iterations of random unitary operations. Although, in general, these quantum operations cannot be diagonalized it is shown that their resulting asymptotic dynamics is described by a diagonalizable superoperator. We prove that this asymptotic dynamics takes place in a typically low dimensional attractor space which is independent of the probability distribution of the unitary operations applied. This vector space is spanned by all eigenvectors of the unitary operations involved which are associated with eigenvalues of unit modulus. Implications for possible asymptotic dynamics of iterated random unitary operations are presented and exemplified in an example involving random controlled-not operations acting on two qubits.
Non-unitary probabilistic quantum computing
Gingrich, Robert M.; Williams, Colin P.
2004-01-01
We present a method for designing quantum circuits that perform non-unitary quantum computations on n-qubit states probabilistically, and give analytic expressions for the success probability and fidelity.
Entanglement quantification by local unitary operations
Energy Technology Data Exchange (ETDEWEB)
Monras, A.; Giampaolo, S. M.; Gualdi, G.; Illuminati, F. [Dipartimento di Matematica e Informatica, Universita degli Studi di Salerno, CNISM, Unita di Salerno, and INFN, Sezione di Napoli-Gruppo Collegato di Salerno, Via Ponte don Melillo, I-84084 Fisciano (Italy); Adesso, G.; Davies, G. B. [School of Mathematical Sciences, University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom)
2011-07-15
Invariance under local unitary operations is a fundamental property that must be obeyed by every proper measure of quantum entanglement. However, this is not the only aspect of entanglement theory where local unitary operations play a relevant role. In the present work we show that the application of suitable local unitary operations defines a family of bipartite entanglement monotones, collectively referred to as ''mirror entanglement.'' They are constructed by first considering the (squared) Hilbert-Schmidt distance of the state from the set of states obtained by applying to it a given local unitary operator. To the action of each different local unitary operator there corresponds a different distance. We then minimize these distances over the sets of local unitary operations with different spectra, obtaining an entire family of different entanglement monotones. We show that these mirror-entanglement monotones are organized in a hierarchical structure, and we establish the conditions that need to be imposed on the spectrum of a local unitary operator for the associated mirror entanglement to be faithful, i.e., to vanish in and only in separable pure states. We analyze in detail the properties of one particularly relevant member of the family, the ''stellar mirror entanglement'' associated with the traceless local unitary operations with nondegenerate spectra and equispaced eigenvalues in the complex plane. This particular measure generalizes the original analysis of S. M. Giampaolo and F. Illuminati [Phys. Rev. A 76, 042301 (2007)], valid for qubits and qutrits. We prove that the stellar entanglement is a faithful bipartite entanglement monotone in any dimension and that it is bounded from below by a function proportional to the linear entropy and from above by the linear entropy itself, coinciding with it in two- and three-dimensional spaces.
Right-unitary transformation theory and applications
Tang, Zhong
1996-01-01
We develop a new transformation theory in quantum physics, where the transformation operators, defined in the infinite dimensional Hilbert space, have right-unitary inverses only. Through several theorems, we discuss the properties of state space of such operators. As one application of the right-unitary transformation (RUT), we show that using the RUT method, we can solve exactly various interactions of many-level atoms with quantized radiation fields, where the energy of atoms can be two le...
Entanglement quantification by local unitary operations
Monras, A.; Adesso, G.; Giampaolo, S. M.; Gualdi, G.; Davies, G. B.; Illuminati, F.
2011-07-01
Invariance under local unitary operations is a fundamental property that must be obeyed by every proper measure of quantum entanglement. However, this is not the only aspect of entanglement theory where local unitary operations play a relevant role. In the present work we show that the application of suitable local unitary operations defines a family of bipartite entanglement monotones, collectively referred to as “mirror entanglement.” They are constructed by first considering the (squared) Hilbert-Schmidt distance of the state from the set of states obtained by applying to it a given local unitary operator. To the action of each different local unitary operator there corresponds a different distance. We then minimize these distances over the sets of local unitary operations with different spectra, obtaining an entire family of different entanglement monotones. We show that these mirror-entanglement monotones are organized in a hierarchical structure, and we establish the conditions that need to be imposed on the spectrum of a local unitary operator for the associated mirror entanglement to be faithful, i.e., to vanish in and only in separable pure states. We analyze in detail the properties of one particularly relevant member of the family, the “stellar mirror entanglement” associated with the traceless local unitary operations with nondegenerate spectra and equispaced eigenvalues in the complex plane. This particular measure generalizes the original analysis of S. M. Giampaolo and F. Illuminati [Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.76.042301 76, 042301 (2007)], valid for qubits and qutrits. We prove that the stellar entanglement is a faithful bipartite entanglement monotone in any dimension and that it is bounded from below by a function proportional to the linear entropy and from above by the linear entropy itself, coinciding with it in two- and three-dimensional spaces.
Creation of ultracold molecules from a Fermi gas of atoms
2003-01-01
Since the realization of Bose-Einstein condensates (BEC) in atomic gases an experimental challenge has been the production of molecular gases in the quantum regime. A promising approach is to create the molecular gas directly from an ultracold atomic gas; for example, atoms in a BEC have been coupled to electronic ground-state molecules through photoassociation as well as through a magnetic-field Feshbach resonance. The availability of atomic Fermi gases provides the exciting prospect of coup...
Thermalization of Gases: A First Principles Approach
Chafin, Clifford
2015-01-01
Previous approaches of emergent thermalization for condensed matter based on typical wavefunctions are extended to generate an intrinsically quantum theory of gases. Gases are fundamentally quantum objects at all temperatures, by virtue of rapid delocalization of their constituents. When there is a sufficiently broad spread in the energy of eigenstates, a well-defined temperature is shown to arise by photon production when the samples are optically thick. This produces a highly accurate approximation to the Planck distribution so that thermalization arises from the initial data as a consequence of purely quantum and unitary dynamics. These results are used as a foil for some common hydrodynamic theory of ultracold gases. It is suggested here that strong history dependence typically remains in these gases and so limits the validity of thermodynamics in their description. These problems are even more profound in the extension of hydrodynamics to such gases when they are optically thin, even when their internal ...
Bahauddin, Shah Mohammad; Mehedi Faruk, Mir
2016-09-01
From the unified statistical thermodynamics of quantum gases, the virial coefficients of ideal Bose and Fermi gases, trapped under generic power law potential are derived systematically. From the general result of virial coefficients, one can produce the known results in d = 3 and d = 2. But more importantly we found that, the virial coefficients of Bose and Fermi gases become identical (except the second virial coefficient, where the sign is different) when the gases are trapped under harmonic potential in d = 1. This result suggests the equivalence between Bose and Fermi gases established in d = 1 (J. Stat. Phys. DOI 10.1007/s10955-015-1344-4). Also, it is found that the virial coefficients of two-dimensional free Bose (Fermi) gas are equal to the virial coefficients of one-dimensional harmonically trapped Bose (Fermi) gas.
Uncertainty relations for general unitary operators
Bagchi, Shrobona; Pati, Arun Kumar
2016-10-01
We derive several uncertainty relations for two arbitrary unitary operators acting on physical states of a Hilbert space. We show that our bounds are tighter in various cases than the ones existing in the current literature. Using the uncertainty relation for the unitary operators, we obtain the tight state-independent lower bound for the uncertainty of two Pauli observables and anticommuting observables in higher dimensions. With regard to the minimum-uncertainty states, we derive the minimum-uncertainty state equation by the analytic method and relate this to the ground-state problem of the Harper Hamiltonian. Furthermore, the higher-dimensional limit of the uncertainty relations and minimum-uncertainty states are explored. From an operational point of view, we show that the uncertainty in the unitary operator is directly related to the visibility of quantum interference in an interferometer where one arm of the interferometer is affected by a unitary operator. This shows a principle of preparation uncertainty, i.e., for any quantum system, the amount of visibility for two general noncommuting unitary operators is nontrivially upper bounded.
Black holes, quantum information, and unitary evolution
Giddings, Steven B
2012-01-01
The unitary crisis for black holes indicates an apparent need to modify local quantum field theory. This paper explores the idea that quantum mechanics and in particular unitarity are fundamental principles, but at the price of familiar locality. Thus, one should seek to parameterize unitary evolution, extending the field theory description of black holes, such that their quantum information is transferred to the external state. This discussion is set in a broader framework of unitary evolution acting on Hilbert spaces comprising subsystems. Here, various constraints can be placed on the dynamics, based on quantum information-theoretic and other general physical considerations, and one can seek to describe dynamics with "minimal" departure from field theory. While usual spacetime locality may not be a precise concept in quantum gravity, approximate locality seems an important ingredient in physics. In such a Hilbert space approach an apparently "coarser" form of localization can be described in terms of tenso...
Color Energy Of A Unitary Cayley Graph
Directory of Open Access Journals (Sweden)
Adiga Chandrashekar
2014-11-01
Full Text Available Let G be a vertex colored graph. The minimum number χ(G of colors needed for coloring of a graph G is called the chromatic number. Recently, Adiga et al. [1] have introduced the concept of color energy of a graph Ec(G and computed the color energy of few families of graphs with χ(G colors. In this paper we derive explicit formulas for the color energies of the unitary Cayley graph Xn, the complement of the colored unitary Cayley graph (Xnc and some gcd-graphs.
Boundary Relations, Unitary Colligations, and Functional Models
Behrndt, Jussi; Hassi, Seppo; de Snoo, Henk
2009-01-01
Recently a new notion, the so-called boundary relation, has been introduced involving an analytic object, the so-called Weyl family. Weyl families and boundary relations establish a link between the class of Nevanlinna families and unitary relations acting from one Krein in space, a basic (state) sp
Developmental Dyspraxia: Is It a Unitary Function?
Ayres, A. Jean; And Others
1987-01-01
A group of 182 children (ages four through nine) with known or suspected sensory integrative dysfunction were assessed using tests and clinical observations to examine developmental dyspraxia. The study did not justify the existence of either a unitary function or different types of developmental dyspraxia. (Author/CH)
Dirac cohomology of unitary representations of equal rank exceptional groups
Institute of Scientific and Technical Information of China (English)
2007-01-01
In this paper, we consider the unitary representations of equal rank exceptional groups of type E with a regular lambda-lowest K-type and classify those unitary representations with the nonzero Dirac cohomology.
Neutron matter at low density and the unitary limit
Baldo, M
2007-01-01
Neutron matter at low density is studied within the hole-line expansion. Calculations are performed in the range of Fermi momentum $k_F$ between 0.4 and 0.8 fm$^{-1}$. It is found that the Equation of State is determined by the $^1S_0$ channel only, the three-body forces contribution is quite small, the effect of the single particle potential is negligible and the three hole-line contribution is below 5% of the total energy and indeed vanishing small at the lowest densities. Despite the unitary limit is actually never reached, the total energy stays very close to one half of the free gas value throughout the considered density range. A rank one separable representation of the bare NN interaction, which reproduces the physical scattering length and effective range, gives results almost indistinguishable from the full Brueckner G-matrix calculations with a realistic force. The extension of the calculations below $k_F = 0.4$ fm$^{-1}$ does not indicate any pathological behavior of the neutron Equation of State.
Quantum phases of Fermi-Fermi mixtures in optical lattices
Iskin, M.; de Melo, C. A. R. Sa
2007-01-01
The ground state phase diagram of Fermi-Fermi mixtures in optical lattices is analyzed as a function of interaction strength, population imbalance, filling fraction and tunneling parameters. It is shown that population imbalanced Fermi-Fermi mixtures reduce to strongly interacting Bose-Fermi mixtures in the molecular limit, in sharp contrast to homogeneous or harmonically trapped systems where the resulting Bose-Fermi mixture is weakly interacting. Furthermore, insulating phases are found in ...
Pseudo-random unitary operators for quantum information processing.
Emerson, Joseph; Weinstein, Yaakov S; Saraceno, Marcos; Lloyd, Seth; Cory, David G
2003-12-19
In close analogy to the fundamental role of random numbers in classical information theory, random operators are a basic component of quantum information theory. Unfortunately, the implementation of random unitary operators on a quantum processor is exponentially hard. Here we introduce a method for generating pseudo-random unitary operators that can reproduce those statistical properties of random unitary operators most relevant to quantum information tasks. This method requires exponentially fewer resources, and hence enables the practical application of random unitary operators in quantum communication and information processing protocols. Using a nuclear magnetic resonance quantum processor, we were able to realize pseudorandom unitary operators that reproduce the expected random distribution of matrix elements.
Identical Wells, Symmetry Breaking, and the Near-Unitary Limit
Harshman, N. L.
2017-03-01
Energy level splitting from the unitary limit of contact interactions to the near unitary limit for a few identical atoms in an effectively one-dimensional well can be understood as an example of symmetry breaking. At the unitary limit in addition to particle permutation symmetry there is a larger symmetry corresponding to exchanging the N! possible orderings of N particles. In the near unitary limit, this larger symmetry is broken, and different shapes of traps break the symmetry to different degrees. This brief note exploits these symmetries to present a useful, geometric analogy with graph theory and build an algebraic framework for calculating energy splitting in the near unitary limit.
Transition from Poisson to circular unitary ensemble
Indian Academy of Sciences (India)
Vinayak; Akhilesh Pandey
2009-09-01
Transitions to universality classes of random matrix ensembles have been useful in the study of weakly-broken symmetries in quantum chaotic systems. Transitions involving Poisson as the initial ensemble have been particularly interesting. The exact two-point correlation function was derived by one of the present authors for the Poisson to circular unitary ensemble (CUE) transition with uniform initial density. This is given in terms of a rescaled symmetry breaking parameter Λ. The same result was obtained for Poisson to Gaussian unitary ensemble (GUE) transition by Kunz and Shapiro, using the contour-integral method of Brezin and Hikami. We show that their method is applicable to Poisson to CUE transition with arbitrary initial density. Their method is also applicable to the more general ℓ CUE to CUE transition where CUE refers to the superposition of ℓ independent CUE spectra in arbitrary ratio.
Complete Pick Positivity and Unitary Invariance
Bhattacharya, Angshuman
2009-01-01
The characteristic function for a contraction is a classical complete unitary invariant devised by Sz.-Nagy and Foias. Just as a contraction is related to the Szego kernel $k_S(z,w) = (1 - z\\ow)^{-1}$ for $|z|, |w| < 1$, by means of $(1/k_S)(T,T^*) \\ge 0$, we consider an arbitrary open connected domain $\\Omega$ in $\\BC^n$, a complete Nevanilinna-Pick kernel $k$ on $\\Omega$ and a tuple $T = (T_1, ..., T_n)$ of commuting bounded operators on a complex separable Hilbert space $\\clh$ such that $(1/k)(T,T^*) \\ge 0$. For a complete Pick kernel the $1/k$ functional calculus makes sense in a beautiful way. It turns out that the model theory works very well and a characteristic function can be associated with $T$. Moreover, the characteristic function then is a complete unitary invariant for a suitable class of tuples $T$.
Quantum Mutual Information Along Unitary Orbits
Jevtic, Sania; Rudolph, Terry
2011-01-01
Motivated by thermodynamic considerations, we analyse the variation of the quantum mutual information on a unitary orbit of a bipartite system state, with and without global constraints such as energy conservation. We solve the full optimisation problem for the smallest system of two qubits, and explore thoroughly the effect of unitary operations on the space of reduced-state spectra. We then provide applications of these ideas to physical processes within closed quantum systems, such as a generalized collision model approach to thermal equilibrium and a global Maxwell demon playing tricks on local observers. For higher dimensions, the maximization of correlations is relatively straightforward, however the minimisation of correlations displays non-trivial structures. We characterise a set of separable states in which the minimally correlated state resides, and find a collection of classically correlated states admitting a particular "Young tableau" form. Furthermore, a partial order exists on this set with re...
On unitary reconstruction of linear optical networks
Tillmann, Max; Walther, Philip
2015-01-01
Linear optical elements are pivotal instruments in the manipulation of classical and quantum states of light. The vast progress in integrated quantum photonic technology enables the implementation of large numbers of such elements on chip while providing interferometric stability. As a trade-off these structures face the intrinsic challenge of characterizing their optical transformation as individual optical elements are not directly accessible. Thus the unitary transformation needs to be reconstructed from a dataset generated with having access to the input and output ports of the device only. Here we present a novel approach to unitary reconstruction that significantly improves upon existing approaches. We compare its performance to several approaches via numerical simulations for networks up to 14 modes. We show that an adapted version of our approach allows to recover all mode-dependent losses and to obtain highest reconstruction fidelities under such conditions.
Unitary and room air-conditioners
Energy Technology Data Exchange (ETDEWEB)
Christian, J.E.
1977-09-01
The scope of this technology evaluation on room and unitary air conditioners covers the initial investment and performance characteristics needed for estimating the operating cost of air conditioners installed in an ICES community. Cooling capacities of commercially available room air conditioners range from 4000 Btu/h to 36,000 Btu/h; unitary air conditioners cover a range from 6000 Btu/h to 135,000 Btu/h. The information presented is in a form useful to both the computer programmer in the construction of a computer simulation of the packaged air-conditioner's performance and to the design engineer, interested in selecting a suitably sized and designed packaged air conditioner.
Scalable Noise Estimation with Random Unitary Operators
Emerson, J; Zyczkowski, K; Emerson, Joseph; Alicki, Robert; Zyczkowski, Karol
2005-01-01
We describe a scalable stochastic method for the experimental measurement of generalized fidelities characterizing the accuracy of the implementation of a coherent quantum transformation. The method is based on the motion reversal of random unitary operators. In the simplest case our method enables direct estimation of the average gate fidelity. The more general fidelities are characterized by a universal exponential rate of fidelity loss. In all cases the measurable fidelity decrease is directly related to the strength of the noise affecting the implementation -- quantified by the trace of the superoperator describing the non--unitary dynamics. While the scalability of our stochastic protocol makes it most relevant in large Hilbert spaces (when quantum process tomography is infeasible), our method should be immediately useful for evaluating the degree of control that is achievable in any prototype quantum processing device. By varying over different experimental arrangements and error-correction strategies a...
Scalable noise estimation with random unitary operators
Energy Technology Data Exchange (ETDEWEB)
Emerson, Joseph [Perimeter Institute for Theoretical Physics, Waterloo, ON (Canada); Alicki, Robert [Institute of Theoretical Physics and Astrophysics, University of Gdansk, Wita Stwosza 57, PL 80-952 Gdansk (Poland); Zyczkowski, Karol [Perimeter Institute for Theoretical Physics, Waterloo, ON (Canada)
2005-10-01
We describe a scalable stochastic method for the experimental measurement of generalized fidelities characterizing the accuracy of the implementation of a coherent quantum transformation. The method is based on the motion reversal of random unitary operators. In the simplest case our method enables direct estimation of the average gate fidelity. The more general fidelities are characterized by a universal exponential rate of fidelity loss. In all cases the measurable fidelity decrease is directly related to the strength of the noise affecting the implementation, quantified by the trace of the superoperator describing the non-unitary dynamics. While the scalability of our stochastic protocol makes it most relevant in large Hilbert spaces (when quantum process tomography is infeasible), our method should be immediately useful for evaluating the degree of control that is achievable in any prototype quantum processing device. By varying over different experimental arrangements and error-correction strategies, additional information about the noise can be determined.
Generalized Unitaries and the Picard Group
Indian Academy of Sciences (India)
Michael Skeide
2006-11-01
After discussing some basic facts about generalized module maps, we use the representation theory of the algebra $\\mathscr{B}^a(E)$ of adjointable operators on a Hilbert $\\mathcal{B}$-module to show that the quotient of the group of generalized unitaries on and its normal subgroup of unitaries on is a subgroup of the group of automorphisms of the range ideal $\\mathcal{B}_E$ of in $\\mathcal{B}$. We determine the kernel of the canonical mapping into the Picard group of $\\mathcal{B}_E$ in terms of the group of quasi inner automorphisms of $\\mathcal{B}_E$. As a by-product we identify the group of bistrict automorphisms of the algebra of adjointable operators on modulo inner automorphisms as a subgroup of the (opposite of the) Picard group.
Recurrence for discrete time unitary evolutions
Grünbaum, F A; Werner, A H; Werner, R F
2012-01-01
We consider quantum dynamical systems specified by a unitary operator U and an initial state vector \\phi. In each step the unitary is followed by a projective measurement checking whether the system has returned to the initial state. We call the system recurrent if this eventually happens with probability one. We show that recurrence is equivalent to the absence of an absolutely continuous part from the spectral measure of U with respect to \\phi. We also show that in the recurrent case the expected first return time is an integer or infinite, for which we give a topological interpretation. A key role in our theory is played by the first arrival amplitudes, which turn out to be the (complex conjugated) Taylor coefficients of the Schur function of the spectral measure. On the one hand, this provides a direct dynamical interpretation of these coefficients; on the other hand it links our definition of first return times to a large body of mathematical literature.
Integral Compressor/Generator/Fan Unitary Structure
Dreiman, Nelik
2016-01-01
INTEGRAL COMPRESSOR / GENERATOR / FAN UNITARY STRUCTURE.*) Dr. Nelik Dreiman Consultant, P.O.Box 144, Tipton, MI E-mail: An extremely compact, therefore space saving single compressor/generator/cooling fan structure of short axial length and light weight has been developed to provide generation of electrical power with simultaneous operation of the compressor when power is unavailable or function as a regular AC compressor powered by a power line. The generators and ai...
Unitary representations and harmonic analysis an introduction
Sugiura, M
1990-01-01
The principal aim of this book is to give an introduction to harmonic analysis and the theory of unitary representations of Lie groups. The second edition has been brought up to date with a number of textual changes in each of the five chapters, a new appendix on Fatou''s theorem has been added in connection with the limits of discrete series, and the bibliography has been tripled in length.
Apostol, M
2001-01-01
sup 3 He liquefies at 3.2 K under normal pressure, where its mean inter-particle separation of a few angstroms, is comparable with the range of the interaction potential (and with the mean inter-particle separation in the corresponding ideal gas); its thermal wavelength is about 8 A, so that, under this conditions, sup 3 He is a quantum liquid of fermions, or a Fermi liquid (sometimes called a normal Fermi liquid too). The motion of the sup 3 He atoms in the (repulsive) self-consistent, meanfield potential is affected by inertial effects, i.e. the particles possess an effective mass, and consequently they obey the Fermi distribution, like an ideal Fermi gas. In this paper the Landau's theory of the Fermi liquid is reviewed. (author)
Optimal control theory for unitary transformations
Palao, J P; Palao, Jose P.
2003-01-01
The dynamics of a quantum system driven by an external field is well described by a unitary transformation generated by a time dependent Hamiltonian. The inverse problem of finding the field that generates a specific unitary transformation is the subject of study. The unitary transformation which can represent an algorithm in a quantum computation is imposed on a subset of quantum states embedded in a larger Hilbert space. Optimal control theory (OCT) is used to solve the inversion problem irrespective of the initial input state. A unified formalism, based on the Krotov method is developed leading to a new scheme. The schemes are compared for the inversion of a two-qubit Fourier transform using as registers the vibrational levels of the $X^1\\Sigma^+_g$ electronic state of Na$_2$. Raman-like transitions through the $A^1\\Sigma^+_u$ electronic state induce the transitions. Light fields are found that are able to implement the Fourier transform within a picosecond time scale. Such fields can be obtained by pulse-...
Meulenbelt, J
2016-01-01
Acute inhalation injury can result from the use of household cleaning agents (e.g. chlorine, ammonia), industrial or combustion gases (e.g. sulfur dioxide, nitrogen oxides) or bioterrorism. The severity of the injury is to a great extent determined by the circumstances of exposure. If exposure was i
... life. Governments all around the world ban and control production and use of several industrial gases that destroy atmospheric ozone and create a hole in the ozone layer . At lower elevations of the atmosphere (the troposphere), ozone is harmful to ... for Future Emissions FAQs How much carbon dioxide is produced when ...
Meulenbelt, J
Acute inhalation injury can result from the use of household cleaning agents (e.g. chlorine, ammonia), industrial or combustion gases (e.g. sulfur dioxide, nitrogen oxides) or bioterrorism. The severity of the injury is to a great extent determined by the circumstances of exposure. If exposure was
Stable unitary integrators for the numerical implementation of continuous unitary transformations
Savitz, Samuel; Refael, Gil
2017-09-01
The technique of continuous unitary transformations has recently been used to provide physical insight into a diverse array of quantum mechanical systems. However, the question of how to best numerically implement the flow equations has received little attention. The most immediately apparent approach, using standard Runge-Kutta numerical integration algorithms, suffers from both severe inefficiency due to stiffness and the loss of unitarity. After reviewing the formalism of continuous unitary transformations and Wegner's original choice for the infinitesimal generator of the flow, we present a number of approaches to resolving these issues including a choice of generator which induces what we call the "uniform tangent decay flow" and three numerical integrators specifically designed to perform continuous unitary transformations efficiently while preserving the unitarity of flow. We conclude by applying one of the flow algorithms to a simple calculation that visually demonstrates the many-body localization transition.
Bosonic models with Fermi-liquid kinematics: realizations and properties
Goldbart, Paul; Gopalakrishnan, Sarang; Lamacraft, Austen
2011-03-01
We consider models of interacting bosons in which the single-particle kinetic energy achieves its minimum on a surface in momentum space. The kinematics of such models resembles that resulting from Pauli blocking in Fermi liquids; therefore, Shankar's renormalization-group treatment of Fermi liquids can be adapted to investigate phase transitions in these bosonic systems. We explore possible experimental realizations of such models in cold atomic gases: e.g., via spin-orbit coupling, multimode-cavity-mediated interactions, and Cooper pairing of Fermi gases in spin-dependent lattices. We address the phase structure and critical behavior of the resulting models within the framework of Ref., focusing in particular on Bose-Einstein condensation and on quantum versions of the Brazovskii transition from a superfluid to a supersolid.
Adams, Allan; Carr, Lincoln D.; Schaefer, Thomas; Steinberg, Peter; Thomas, John E.
2013-04-01
The last few years have witnessed a dramatic convergence of three distinct lines of research concerned with different kinds of extreme quantum matter. Two of these involve new quantum fluids that can be studied in the laboratory, ultracold quantum gases and quantum chromodynamics (QCD) plasmas. Even though these systems involve vastly different energy scales, the physical properties of the two quantum fluids are remarkably similar. The third line of research is based on the discovery of a new theoretical tool for investigating the properties of extreme quantum matter, holographic dualties. The main goal of this focus issue is to foster communication and understanding between these three fields. We proceed to describe each in more detail. Ultracold quantum gases offer a new paradigm for the study of nonperturbative quantum many-body physics. With widely tunable interaction strength, spin composition, and temperature, using different hyperfine states one can model spin-1/2 fermions, spin-3/2 fermions, and many other spin structures of bosons, fermions, and mixtures thereof. Such systems have produced a revolution in the study of strongly interacting Fermi systems, for example in the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) crossover region, where a close collaboration between experimentalists and theorists—typical in this field—enabled ground-breaking studies in an area spanning several decades. Half-way through this crossover, when the scattering length characterizing low-energy collisions diverges, one obtains a unitary quantum gas, which is universal and scale invariant. The unitary gas has close parallels in the hydrodynamics of QCD plasmas, where the ratio of viscosity to entropy density is extremely low and comparable to the minimum viscosity conjecture, an important prediction of AdS/CFT (see below). Exciting developments in the thermodynamic and transport properties of strongly interacting Fermi gases are of broad
Byers, N
2002-01-01
This talk is about Enrico Fermi and Leo Szilard, their collaboration and involvement in nuclear energy development and decisions to construct and use the atomic bomb in World War II. Fermi and Szilard worked closely together at Columbia in 1939-40 to explore feasibility of a nuclear chain reaction, and then on the physics for construction of the first pile (nuclear reactor). "On matters scientific or technical there was rarely any disagreement between Fermi and myself" Szilard said. But there were sharp differences on other matters.
NASA
2009-01-01
1. This view from NASA's Fermi Gamma-ray Space Telescope is the deepest and best-resolved portrait of the gamma-ray sky to date. The image shows how the sky appears at energies more than 150 million times greater than that of visible light. Among the signatures of bright pulsars and active galaxies is something familiar -- a faint path traced by the sun. (Credit: NASA/DOE/Fermi LAT Collaboration) 2. The Large Area Telescope (LAT) on Fermi detects gamma-rays through matter (electrons) and antimatter (positrons) they produce after striking layers of tungsten. (Credit: NASA/Goddard Space Flight Center Conceptual Image Lab)
Podosek, F. A.
2003-12-01
The noble gases are the group of elements - helium, neon, argon, krypton, xenon - in the rightmost column of the periodic table of the elements, those which have "filled" outermost shells of electrons (two for helium, eight for the others). This configuration of electrons results in a neutral atom that has relatively low electron affinity and relatively high ionization energy. In consequence, in most natural circumstances these elements do not form chemical compounds, whence they are called "noble." Similarly, much more so than other elements in most circumstances, they partition strongly into a gas phase (as monatomic gas), so that they are called the "noble gases" (also, "inert gases"). (It should be noted, of course, that there is a sixth noble gas, radon, but all isotopes of radon are radioactive, with maximum half-life a few days, so that radon occurs in nature only because of recent production in the U-Th decay chains. The factors that govern the distribution of radon isotopes are thus quite different from those for the five gases cited. There are interesting stories about radon, but they are very different from those about the first five noble gases, and are thus outside the scope of this chapter.)In the nuclear fires in which the elements are forged, the creation and destruction of a given nuclear species depends on its nuclear properties, not on whether it will have a filled outermost shell when things cool off and nuclei begin to gather electrons. The numerology of nuclear physics is different from that of chemistry, so that in the cosmos at large there is nothing systematically special about the abundances of the noble gases as compared to other elements. We live in a very nonrepresentative part of the cosmos, however. As is discussed elsewhere in this volume, the outstanding generalization about the geo-/cosmochemistry of the terrestrial planets is that at some point thermodynamic conditions dictated phase separation of solids from gases, and that the
National Aeronautics and Space Administration — All analysis results presented here are preliminary and are not intended as an official catalog of Fermi-LAT detected GRBs. Please consult the table's caveat page...
National Aeronautics and Space Administration — Fermi is a powerful space observatory that will open a wide window on the universe. Gamma rays are the highest-energy form of light, and the gamma-ray sky is...
On unitary representability of topological groups
Galindo Pastor, Jorge
2006-01-01
We prove that the additive group $(E^\\ast,\\tau_k(E))$ of an $\\mathscr{L}_\\infty$-Banach space $E$, with the topology $\\tau_k(E)$ of uniform convergence on compact subsets of $E$, is topologically isomorphic to a subgroup of the unitary group of some Hilbert space (is \\emph{unitarily representable}). This is the same as proving that the topological group $(E^\\ast,\\tau_k(E))$ is uniformly homeomorphic to a subset of $\\ell_2^\\kappa$ for some $\\kappa$. As an immediate consequence, preduals of com...
Quantum remote control Teleportation of unitary operations
Huelga, S F; Chefles, A; Plenio, M B
2001-01-01
We consider the implementation of an unknown arbitrary unitary operation U upon a distant quantum system. This teleportation of U can be viewed as a quantum remote control. We investigate the protocols which achieve this using local operations, classical communication and shared entanglement (LOCCSE). Lower bounds on the necessary entanglement and classical communication are determined using causality and the linearity of quantum mechanics. We examine in particular detail the resources required if the remote control is to be implemented as a classical black box. Under these circumstances, we prove that the required resources are, necessarily, those needed for implementation by bidirectional state teleportation.
Unitary Gas Constraints on Nuclear Symmetry Energy
Kolomeitsev, Evgeni E; Ohnishi, Akira; Tews, Ingo
2016-01-01
We show the existence of a lower bound on the volume symmetry energy parameter $S_0$ from unitary gas considerations. We further demonstrate that values of $S_0$ above this minimum imply upper and lower bounds on the symmetry energy parameter $L$ describing its lowest-order density dependence. The bounds are found to be consistent with both recent calculations of the energies of pure neutron matter and constraints from nuclear experiments. These results are significant because many equations of state in active use for simulations of nuclear structure, heavy ion collisions, supernovae, neutron star mergers, and neutron star structure violate these constraints.
Universal dynamics in a Unitary Bose Gas
Klauss, Catherine; Xie, Xin; D'Incao, Jose; Jin, Deborah; Cornell, Eric
2016-05-01
We investigate the dynamics of a unitary Bose gas with an 85 Rb BEC, specifically to determine whether the dynamics scale universally with density. We find that the initial density affects both the (i) projection of the strongly interacting many-body wave-function onto the Feshbach dimer state when the system is rapidly ramped to a weakly interacting value of the scattering length a and (ii) the overall decay rate to deeper bound states. We will present data on both measurements across two orders of magnitude in density, and will discuss how the data illustrate the competing roles of universality and Efimov physics.
Unitary Quantum Lattice Algorithms for Turbulence
2016-05-23
collision operator, based on the 3D relativistic Dirac particle dynamics theory of Yepez, ĈD = cosθ x( ) −i sinθ x( ) −i sinθ x( ) cosθ x... based algorithm it will result in a finite difference representation of the GP Eq. (24) provided the parameters are so chosen to yield diffusion-like...Fluid Dynamics, ed. H. W. Oh, ( InTech Publishers, Croatia, 2012) [20] “Unitary qubit lattice simulations of complex vortex structures
Unitary water-to-air heat pumps
Energy Technology Data Exchange (ETDEWEB)
Christian, J.E.
1977-10-01
Performance and cost functions for nine unitary water-to-air heat pumps ranging in nominal size from /sup 1///sub 2/ to 26 tons are presented in mathematical form for easy use in heat pump computer simulations. COPs at nominal water source temperature of 60/sup 0/F range from 2.5 to 3.4 during the heating cycle; during the cooling cycle EERs range from 8.33 to 9.09 with 85/sup 0/F entering water source temperatures. The COP and EER values do not include water source pumping power or any energy requirements associated with a central heat source and heat rejection equipment.
Quantum mechanics with non-unitary symmetries
Bistrovic, B
2000-01-01
This article shows how to properly extend symmetries of non-relativistic quantum mechanics to include non-unitary representations of Lorentz group for all spins. It follows from this that (almost) all existing relativistic single particle Lagrangians and equations are incorrect. This is shown in particular for Dirac's equation and Proca equations. It is shown that properly constructed relativistic extensions have no negative energies, zitterbewegung effects and have proper symmetric energy-momentum tensor and angular momentum density tensor. The downside is that states with negative norm are inevitable in all representations.
Unitary appreciative inquiry: evolution and refinement.
Cowling, W Richard; Repede, Elizabeth
2010-01-01
Unitary appreciative inquiry (UAI), developed over the past 20 years, provides an orientation and process for uncovering human wholeness and discovering life patterning in individuals and groups. Refinements and a description of studies using UAI are presented. Assumptions and conceptual underpinnings of the method distinguishing its contributions from other methods are reported. Data generation strategies that capture human wholeness and elucidate life patterning are proposed. Data synopsis as an alternative to analysis is clarified and explicated. Standards that suggest enhancing the legitimacy of knowledge and credibility of research are specified. Potential expansions of UAI offer possibilities for extending epistemologies, aesthetic integration, and theory development.
Asymptotic expansions for the Gaussian unitary ensemble
DEFF Research Database (Denmark)
Haagerup, Uffe; Thorbjørnsen, Steen
2012-01-01
Let g : R ¿ C be a C8-function with all derivatives bounded and let trn denote the normalized trace on the n × n matrices. In Ref. 3 Ercolani and McLaughlin established asymptotic expansions of the mean value ¿{trn(g(Xn))} for a rather general class of random matrices Xn, including the Gaussian...... Unitary Ensemble (GUE). Using an analytical approach, we provide in the present paper an alternative proof of this asymptotic expansion in the GUE case. Specifically we derive for a random matrix Xn that where k is an arbitrary positive integer. Considered as mappings of g, we determine the coefficients...
Endoscopic classification of representations of quasi-split unitary groups
Mok, Chung Pang
2015-01-01
In this paper the author establishes the endoscopic classification of tempered representations of quasi-split unitary groups over local fields, and the endoscopic classification of the discrete automorphic spectrum of quasi-split unitary groups over global number fields. The method is analogous to the work of Arthur on orthogonal and symplectic groups, based on the theory of endoscopy and the comparison of trace formulas on unitary groups and general linear groups.
Enrico Fermi centenary exhibition seminar
Maximilien Brice
2002-01-01
Photo 01: Dr. Juan Antonio Rubio, Leader of the Education and Technology Transfer Division and CERN Director General, Prof. Luciano Maiani. Photo 03: Luciano Maiani, Welcome and Introduction Photo 09: Antonino Zichichi, The New 'Centro Enrico Fermi' at Via Panisperna Photos 10, 13: Ugo Amaldi, Fermi at Via Panisperna and the birth of Nuclear Medicine Photo 14: Jack Steinberger, Fermi in Chicago Photo 18: Valentin Telegdi, A close-up of Fermi Photo 21: Arnaldo Stefanini, Celebrating Fermi's Centenary in Documents and Pictures.
Super-allowed Fermi beta-decay revisited
Wilkinson, D H
2002-01-01
Analysis of J suppi=0 sup +->0 sup + super-allowed Fermi transitions is limited with respect to the precision of its outcome in terms of the Fermi coupling constant neither by the accuracy of the experimental input data nor by the confidence with which the radiative corrections can be applied but rather by knowledge of the nuclear mismatch: the subversion of isospin symmetry along the multiplets. Theoretical estimates of this mismatch differ considerably from to their direct nuclide-by-nuclide application results in an apparent clear violation of the hypothesis of conservation of the vector current and evident inconsistency with unitary of the Cabibbo-Kobayashi-Maskawa matrix. This paper pursues and elaborates the earlier suggestion that, in these unsatisfactory circumstances, the best procedure is to look to the experimental data themselves to determine and eliminate the mismatch by appropriate extrapolation to Z approx 0 where the mismatch falls away. This is done: (i) without any prior correction for misma...
Phase space methods for degenerate quantum gases
Dalton, Bryan J; Barnett, Stephen M
2015-01-01
Recent experimental progress has enabled cold atomic gases to be studied at nano-kelvin temperatures, creating new states of matter where quantum degeneracy occurs - Bose-Einstein condensates and degenerate Fermi gases. Such quantum states are of macroscopic dimensions. This book presents the phase space theory approach for treating the physics of degenerate quantum gases, an approach already widely used in quantum optics. However, degenerate quantum gases involve massive bosonic and fermionic atoms, not massless photons. The book begins with a review of Fock states for systems of identical atoms, where large numbers of atoms occupy the various single particle states or modes. First, separate modes are considered, and here the quantum density operator is represented by a phase space distribution function of phase space variables which replace mode annihilation, creation operators, the dynamical equation for the density operator determines a Fokker-Planck equation for the distribution function, and measurable...
Right-unitary transformation theory and applications
Tang, Z
1996-01-01
We develop a new transformation theory in quantum physics, where the transformation operators, defined in the infinite dimensional Hilbert space, have right-unitary inverses only. Through several theorems, we discuss the properties of state space of such operators. As one application of the right-unitary transformation (RUT), we show that using the RUT method, we can solve exactly various interactions of many-level atoms with quantized radiation fields, where the energy of atoms can be two levels, three levels in Lambda, V and equiv configurations, and up to higher (>3) levels. These interactions have wide applications in atomic physics, quantum optics and quantum electronics. In this paper, we focus on two typical systems: one is a two-level generalized Jaynes-Cummings model, where the cavity field varies with the external source; the other one is the interaction of three-level atom with quantized radiation fields, where the atoms have Lambda-configuration energy levels, and the radiation fields are one-mode...
Enrico Fermi exhibition at CERN
2002-01-01
A touring exhibition celebrating the centenary of Enrico Fermi's birth in 1901 will be on display at CERN (Main Building, Mezzanine) from 12-27 September. You are cordially invited to the opening celebration on Thursday 12 September at 16:00 (Main Building, Council Chamber), which will include speechs from: Luciano Maiani Welcome and Introduction Arnaldo Stefanini Celebrating Fermi's Centenary in Documents and Pictures Antonino Zichichi The New 'Centro Enrico Fermi' at Via Panisperna Ugo Amaldi Fermi at Via Panisperna and the birth of Nuclear Medicine Jack Steinberger Fermi in Chicago Valentin Telegdi A Close-up of Fermi and the screening of a documentary video about Fermi: Scienziati a Pisa: Enrico Fermi (Scientists at Pisa: Enrico Fermi) created by Francesco Andreotti for La Limonaia from early film, photographs and sound recordings (In Italian, with English subtitles - c. 30 mins). This will be followed by an aperitif on the Mezz...
Perfect state transfer in unitary Cayley graphs over local rings
Directory of Open Access Journals (Sweden)
Yotsanan Meemark
2014-12-01
Full Text Available In this work, using eigenvalues and eigenvectors of unitary Cayley graphs over finite local rings and elementary linear algebra, we characterize which local rings allowing PST occurring in its unitary Cayley graph. Moreover, we have some developments when $R$ is a product of local rings.
2009-01-01
In only 10 months of scientific activity, the Fermi space observatory has already collected an unprecedented wealth of information on some of the most amazing objects in the sky. In a recent talk at CERN, Luca Latronico, a member of the Fermi collaboration, explained some of their findings and emphasized the strong links between High Energy Physics (HEP) and High Energy Astrophysics (HEA). The Fermi gamma-ray telescope was launched by NASA in June 2008. After about two months of commissioning it started sending significant data back to the Earth. Since then, it has made observations that are changing our view of the sky: from discovering a whole new set of pulsars, the greatest total energy gamma-ray burst ever, to detecting an unexplained abundance of high-energy electrons that could be a signature of dark matter, to producing a uniquely rich and high definition sky map in gamma-rays. The high performance of the instrument comes as ...
D'Agostini, G
2005-01-01
It is curious to learn that Enrico Fermi knew how to base probabilistic inference on Bayes theorem, and that some influential notes on statistics for physicists stem from what the author calls elsewhere, but never in these notes, {\\it the Bayes Theorem of Fermi}. The fact is curious because the large majority of living physicists, educated in the second half of last century -- a kind of middle age in the statistical reasoning -- never heard of Bayes theorem during their studies, though they have been constantly using an intuitive reasoning quite Bayesian in spirit. This paper is based on recollections and notes by Jay Orear and on Gauss' ``Theoria motus corporum coelestium'', being the {\\it Princeps mathematicorum} remembered by Orear as source of Fermi's Bayesian reasoning.
Energy Technology Data Exchange (ETDEWEB)
Christian, J.E.
1977-07-01
This technology evaluation covers commercially available unitary heat pumps ranging from nominal capacities of 1/sup 1///sub 2/ to 45 tons. The nominal COP of the heat pump models, selected as representative, vary from 2.4 to 2.9. Seasonal COPs for heat pump installations and single-family dwellings are reported to vary from 2.5 to 1.1, depending on climate. For cooling performance, the nominal EER's vary from 6.5 to 8.7. Representative part-load performance curves along with cost estimating and reliability data are provided to aid: (1) the systems design engineer to select suitably sized heat pumps based on life-cycle cost analyses, and (2) the computer programmer to develop a simulation code for heat pumps operating in an Integrated Community Energy System.
Biphoton transmission through non-unitary objects
Reichert, Matthew; Sun, Xiaohang; Fleischer, Jason W
2016-01-01
Losses should be accounted for in a complete description of quantum imaging systems, and yet they are often treated as undesirable and largely neglected. In conventional quantum imaging, images are built up by coincidence detection of spatially entangled photon pairs (biphotons) transmitted through an object. However, as real objects are non-unitary (absorptive), part of the transmitted state contains only a single photon, which is overlooked in traditional coincidence measurements. The single photon part has a drastically different spatial distribution than the two-photon part. It contains information both about the object, and, remarkably, the spatial entanglement properties of the incident biphotons. We image the one- and two-photon parts of the transmitted state using an electron multiplying CCD array both as a traditional camera and as a massively parallel coincidence counting apparatus, and demonstrate agreement with theoretical predictions. This work may prove useful for photon number imaging and lead ...
Unitary Quantum Relativity - (Work in Progress)
Finkelstein, David Ritz
2016-12-01
A quantum universe is expressed as a finite unitary relativistic quantum computer network. Its addresses are subject to quantum superposition as well as its memory. It has no exact mathematical model. It Its Hilbert space of input processes is also a Clifford algebra with a modular architecture of many ranks. A fundamental fermion is a quantum computer element whose quantum address belongs to the rank below. The least significant figures of its address define its spin and flavor. The most significant figures of it adress define its orbital variables. Gauging arises from the same quantification as space-time. This blurs star images only slightly, but perhaps measurably. General relativity is an approximation that splits nature into an emptiness with a high symmetry that is broken by a filling of lower symmetry. Action principles result from self-organization pf the vacuum.
Unitary Quantum Relativity. (Work in Progress)
Finkelstein, David Ritz
2017-01-01
A quantum universe is expressed as a finite unitary relativistic quantum computer network. Its addresses are subject to quantum superposition as well as its memory. It has no exact mathematical model. It Its Hilbert space of input processes is also a Clifford algebra with a modular architecture of many ranks. A fundamental fermion is a quantum computer element whose quantum address belongs to the rank below. The least significant figures of its address define its spin and flavor. The most significant figures of it adress define its orbital variables. Gauging arises from the same quantification as space-time. This blurs star images only slightly, but perhaps measurably. General relativity is an approximation that splits nature into an emptiness with a high symmetry that is broken by a filling of lower symmetry. Action principles result from self-organization pf the vacuum.
Quantum Entanglement Growth under Random Unitary Dynamics
Nahum, Adam; Ruhman, Jonathan; Vijay, Sagar; Haah, Jeongwan
2017-07-01
Characterizing how entanglement grows with time in a many-body system, for example, after a quantum quench, is a key problem in nonequilibrium quantum physics. We study this problem for the case of random unitary dynamics, representing either Hamiltonian evolution with time-dependent noise or evolution by a random quantum circuit. Our results reveal a universal structure behind noisy entanglement growth, and also provide simple new heuristics for the "entanglement tsunami" in Hamiltonian systems without noise. In 1D, we show that noise causes the entanglement entropy across a cut to grow according to the celebrated Kardar-Parisi-Zhang (KPZ) equation. The mean entanglement grows linearly in time, while fluctuations grow like (time )1/3 and are spatially correlated over a distance ∝(time )2/3. We derive KPZ universal behavior in three complementary ways, by mapping random entanglement growth to (i) a stochastic model of a growing surface, (ii) a "minimal cut" picture, reminiscent of the Ryu-Takayanagi formula in holography, and (iii) a hydrodynamic problem involving the dynamical spreading of operators. We demonstrate KPZ universality in 1D numerically using simulations of random unitary circuits. Importantly, the leading-order time dependence of the entropy is deterministic even in the presence of noise, allowing us to propose a simple coarse grained minimal cut picture for the entanglement growth of generic Hamiltonians, even without noise, in arbitrary dimensionality. We clarify the meaning of the "velocity" of entanglement growth in the 1D entanglement tsunami. We show that in higher dimensions, noisy entanglement evolution maps to the well-studied problem of pinning of a membrane or domain wall by disorder.
Quantum Entanglement Growth under Random Unitary Dynamics
Directory of Open Access Journals (Sweden)
Adam Nahum
2017-07-01
Full Text Available Characterizing how entanglement grows with time in a many-body system, for example, after a quantum quench, is a key problem in nonequilibrium quantum physics. We study this problem for the case of random unitary dynamics, representing either Hamiltonian evolution with time-dependent noise or evolution by a random quantum circuit. Our results reveal a universal structure behind noisy entanglement growth, and also provide simple new heuristics for the “entanglement tsunami” in Hamiltonian systems without noise. In 1D, we show that noise causes the entanglement entropy across a cut to grow according to the celebrated Kardar-Parisi-Zhang (KPZ equation. The mean entanglement grows linearly in time, while fluctuations grow like (time^{1/3} and are spatially correlated over a distance ∝(time^{2/3}. We derive KPZ universal behavior in three complementary ways, by mapping random entanglement growth to (i a stochastic model of a growing surface, (ii a “minimal cut” picture, reminiscent of the Ryu-Takayanagi formula in holography, and (iii a hydrodynamic problem involving the dynamical spreading of operators. We demonstrate KPZ universality in 1D numerically using simulations of random unitary circuits. Importantly, the leading-order time dependence of the entropy is deterministic even in the presence of noise, allowing us to propose a simple coarse grained minimal cut picture for the entanglement growth of generic Hamiltonians, even without noise, in arbitrary dimensionality. We clarify the meaning of the “velocity” of entanglement growth in the 1D entanglement tsunami. We show that in higher dimensions, noisy entanglement evolution maps to the well-studied problem of pinning of a membrane or domain wall by disorder.
Solares, H. A. Ayala; Hui, C. M.; Hüntemeyer, P.; collaboration, for the HAWC
2015-01-01
The Fermi Bubbles, which comprise two large and homogeneous regions of spectrally hard gamma-ray emission extending up to $55^{o}$ above and below the Galactic Center, were first noticed in GeV gamma-ray data from the Fermi Telescope in 2010. The mechanism or mechanisms which produce the observed hard spectrum are not understood. Although both hadronic and lep- tonic models can describe the spectrum of the bubbles, the leptonic model can also explain similar structures observed in microwave d...
Two-component Fermi gas in a Harmonic Trap
Yi, X X; Cui, H T; Zhang, C M
2002-01-01
We consider a mixture of two-component Fermi gases at low temperature. The density profile of this degenerate Fermi gas is calculated under the semiclassical approximation. The results show that the fermion-fermion interactions make a large correction to the density profile at low temperature. The phase separation of such a mixture is also discussed for both attractive and repulsive interatomic interactions, and the numerical calculations demonstrate the exist of a stable temperature region $T_{c1}
Thermoelectricity in a junction between interacting cold atomic Fermi gases
Sekera, Tibor; Bruder, Christoph; Belzig, Wolfgang
2016-09-01
A gas of interacting ultracold fermions can be tuned into a strongly interacting regime using a Feshbach resonance. Here, we theoretically study quasiparticle transport in a system of two reservoirs of interacting ultracold fermions on the BCS side of the BCS-BEC crossover coupled weakly via a tunnel junction. Using the generalized BCS theory, we calculate the time evolution of the system that is assumed to be initially prepared in a nonequilibrium state characterized by a particle number imbalance or a temperature imbalance. A number of characteristic features like sharp peaks in quasiparticle currents or transitions between the normal and superconducting states are found. We discuss signatures of the Seebeck and the Peltier effects and the resulting temperature difference of the two reservoirs as a function of the interaction parameter (kFa ) -1. The Peltier effect may lead to an additional cooling mechanism for ultracold fermionic atoms.
Unconventional phases of attractive Fermi gases in synthetic Hall ribbons
Ghosh, Sudeep Kumar; Greschner, Sebastian; Yadav, Umesh K.; Mishra, Tapan; Rizzi, Matteo; Shenoy, Vijay B.
2017-06-01
An innovative way to produce quantum Hall ribbons in a cold atomic system is to use M hyperfine states of atoms in a one-dimensional optical lattice to mimic an additional "synthetic dimension." A notable aspect here is that the SU(M ) symmetric interaction between atoms manifests as "infinite ranged" along the synthetic dimension. We study the many-body physics of fermions with SU(M ) symmetric attractive interactions in this system using a combination of analytical field theoretic and numerical density-matrix renormalization-group methods. We uncover the rich ground-state phase diagram of the system, including unconventional phases such as squished baryon fluids, shedding light on many-body physics in low dimensions. Remarkably, changing the parameters entails interesting crossovers and transition; e.g., we show that increasing the magnetic field (that produces the Hall effect) converts a "ferrometallic" state at low fields to a "squished baryon superfluid" (with algebraic pairing correlations) at high fields. We also show that this system provides a unique opportunity to study quantum phase separation in a multiflavor ultracold fermionic system.
Strongly-Interacting Fermi Gases in Reduced Dimensions
2015-11-16
scholarships or fellowships for further studies in science, mathematics, engineering or technology fields: Student Metrics This section only applies to...difference, which appears to oscillate for N2/N1 ≃ 0.34 for the larger pairing energy Eb. To exam - ine the behavior further, we measure the cut-off
Solares, H A Ayala; Hüntemeyer, P
2015-01-01
The Fermi Bubbles, which comprise two large and homogeneous regions of spectrally hard gamma-ray emission extending up to $55^{o}$ above and below the Galactic Center, were first noticed in GeV gamma-ray data from the Fermi Telescope in 2010. The mechanism or mechanisms which produce the observed hard spectrum are not understood. Although both hadronic and lep- tonic models can describe the spectrum of the bubbles, the leptonic model can also explain similar structures observed in microwave data from the WMAP and Planck satellites. Recent publications show that the spectrum of the Fermi Bubbles is well described by a power law with an exponential cutoff in the energy range of 100MeV to 500GeV. Observing the Fermi Bubbles at higher gamma-ray energies will help constrain the origin of the bubbles. A steeper cutoff will favor a leptonic model. The High Altitude Water Cherenkov (HAWC) Observatory, located 4100m above sea level in Mexico, is designed to measure high-energy gamma rays between 100GeV to 100TeV. With...
Sequential scheme for locally discriminating bipartite unitary operations without inverses
Li, Lvzhou
2017-08-01
Local distinguishability of bipartite unitary operations has recently received much attention. A nontrivial and interesting question concerning this subject is whether there is a sequential scheme for locally discriminating between two bipartite unitary operations, because a sequential scheme usually represents the most economic strategy for discrimination. An affirmative answer to this question was given in the literature, however with two limitations: (i) the unitary operations to be discriminated were limited to act on d ⊗d , i.e., a two-qudit system, and (ii) the inverses of the unitary operations were assumed to be accessible, although this assumption may be unrealizable in experiment. In this paper, we improve the result by removing the two limitations. Specifically, we show that any two bipartite unitary operations acting on dA⊗dB can be locally discriminated by a sequential scheme, without using the inverses of the unitary operations. Therefore, this paper enhances the applicability and feasibility of the sequential scheme for locally discriminating unitary operations.
Quantum Entanglement Growth Under Random Unitary Dynamics
Nahum, Adam; Vijay, Sagar; Haah, Jeongwan
2016-01-01
Characterizing how entanglement grows with time in a many-body system, for example after a quantum quench, is a key problem in non-equilibrium quantum physics. We study this problem for the case of random unitary dynamics, representing either Hamiltonian evolution with time--dependent noise or evolution by a random quantum circuit. Our results reveal a universal structure behind noisy entanglement growth, and also provide simple new heuristics for the `entanglement tsunami' in Hamiltonian systems without noise. In 1D, we show that noise causes the entanglement entropy across a cut to grow according to the celebrated Kardar--Parisi--Zhang (KPZ) equation. The mean entanglement grows linearly in time, while fluctuations grow like $(\\text{time})^{1/3}$ and are spatially correlated over a distance $\\propto (\\text{time})^{2/3}$. We derive KPZ universal behaviour in three complementary ways, by mapping random entanglement growth to: (i) a stochastic model of a growing surface; (ii) a `minimal cut' picture, reminisce...
A unitary test of the Ratios Conjecture
Goes, John; Miller, Steven J; Montague, David; Ninsuwan, Kesinee; Peckner, Ryan; Pham, Thuy
2009-01-01
The Ratios Conjecture of Conrey, Farmer and Zirnbauer predicts the answers to numerous questions in number theory, ranging from n-level densities and correlations to mollifiers to moments and vanishing at the central point. The conjecture gives a recipe to generate these answers, which are believed to be correct up to square-root cancelation. These predictions have been verified, for suitably restricted test functions, for the 1-level density of orthogonal and symplectic families of L-functions. In this paper we verify the conjecture's predictions for the unitary family of all Dirichlet $L$-functions with prime conductor; we show square-root agreement between prediction and number theory if the support of the Fourier transform of the test function is in (-1,1), and for support up to (-2,2) we show agreement up to a power savings in the family's cardinality. The interesting feature in this family (which has not surfaced in previous investigations) is determining what is and what is not a diagonal term in the R...
Quantum metrology with unitary parametrization processes.
Liu, Jing; Jing, Xiao-Xing; Wang, Xiaoguang
2015-02-24
Quantum Fisher information is a central quantity in quantum metrology. We discuss an alternative representation of quantum Fisher information for unitary parametrization processes. In this representation, all information of parametrization transformation, i.e., the entire dynamical information, is totally involved in a Hermitian operator H. Utilizing this representation, quantum Fisher information is only determined by H and the initial state. Furthermore, H can be expressed in an expanded form. The highlights of this form is that it can bring great convenience during the calculation for the Hamiltonians owning recursive commutations with their partial derivative. We apply this representation in a collective spin system and show the specific expression of H. For a simple case, a spin-half system, the quantum Fisher information is given and the optimal states to access maximum quantum Fisher information are found. Moreover, for an exponential form initial state, an analytical expression of quantum Fisher information by H operator is provided. The multiparameter quantum metrology is also considered and discussed utilizing this representation.
Unitary Evolution and Cosmological Fine-Tuning
Carroll, Sean M
2010-01-01
Inflationary cosmology attempts to provide a natural explanation for the flatness and homogeneity of the observable universe. In the context of reversible (unitary) evolution, this goal is difficult to satisfy, as Liouville's theorem implies that no dynamical process can evolve a large number of initial states into a small number of final states. We use the invariant measure on solutions to Einstein's equation to quantify the problems of cosmological fine-tuning. The most natural interpretation of the measure is the flatness problem does not exist; almost all Robertson-Walker cosmologies are spatially flat. The homogeneity of the early universe, however, does represent a substantial fine-tuning; the horizon problem is real. When perturbations are taken into account, inflation only occurs in a negligibly small fraction of cosmological histories, less than $10^{-6.6\\times 10^7}$. We argue that while inflation does not affect the number of initial conditions that evolve into a late universe like our own, it neve...
Precision measurement of the sound velocity in an ultracold fermi gas through the BEC-BCS crossover
Joseph, James Adlai
A trapped Fermi gas near a collisional resonance provides a unique laboratory for testing many-body theories in a variety of fields. The ultracold Fermi gas produced in our lab is comprised of the lowest two spin states of 6Li. At 834 G there is a collisional or Feshbach resonance between the two spin states. The scattering length between trapped atoms of opposing spins far exceeds the interparticle spacing of the gas. On resonance, a strongly interacting, unitary, Fermi gas is created which exhibits universal behavior. The unitary Fermi gas is a prototype for other exotic systems in nature from nuclear matter to neutron stars and high temperature superconductors. For magnetic fields less than 834 G the scattering length is positive, and pairs Fermi atoms can form molecular dimers. These dimers, comprised of two fermions, are bosons. At ultracold temperatures the molecular bosons populate the lowest energy level and form a Bose Einstein Condensate (BEC). For magnetic fields greater than 834G the scattering length between fermions in opposing spin states is negative, like Cooper pairs formed between electrons in a superconductor. The Bardeen, Cooper, and Shriefer (BCS) theory was developed to describe the pairing effect in the context of superconductors. In our experiment we produce an ultracold unitary gas. By tuning the magnetic field to either side of the Feshbach resonance we can transform the gas into a weakly interacting BEC or BCS superfluid. Therefore, the region near a Feshbach resonance is called the BEC-BCS crossover. This dissertation presents a precision measurement of the hydrodynamic sound velocity in an ultracold Fermi gas near a Feshbach resonance. The sound velocity is measured at various magnetic fields both above and below resonance. Moreover, we are able compare our measurements to theoretical descriptions of hydrodynamic sound propagation. Further, our measurement of sound velocity exactly reproduces the non-perturbative case, eliminating the
Shah, Kushal; Rom-Kedar, Vered; Turaev, Dmitry
2015-01-01
A Fermi accelerator is a billiard with oscillating walls. A leaky accelerator interacts with an environment of an ideal gas at equilibrium by exchange of particles through a small hole on its boundary. Such interaction may heat the gas: we estimate the net energy flow through the hole under the assumption that the particles inside the billiard do not collide with each other and remain in the accelerator for sufficiently long time. The heat production is found to depend strongly on the type of the Fermi accelerator. An ergodic accelerator, i.e. one which has a single ergodic component, produces a weaker energy flow than a multi-component accelerator. Specifically, in the ergodic case the energy gain is independent of the hole size, whereas in the multi-component case the energy flow may be significantly increased by shrinking the hole size.
Decomposition of Unitary Matrices for Finding Quantum Circuits
Daskin, Anmer
2010-01-01
Constructing appropriate unitary matrix operators for new quantum algorithms and finding the minimum cost gate sequences for the implementation of these unitary operators is of fundamental importance in the field of quantum information and quantum computation. Here, we use the group leaders optimization algorithm, which is an effective and simple global optimization algorithm, to decompose a given unitary matrix into a proper-minimum cost quantum gate sequence. Using this procedure, we present new circuit designs for the simulation of the Toffoli gate, the amplification step of the Grover search algorithm, the quantum Fourier transform, the sender part of the quantum teleportation and the Hamiltonian for the Hydrogen molecule. In addition, we give two algorithmic methods for the construction of unitary matrices with respect to the different types of the quantum control gates. Our results indicate that the procedure is effective, general, and easy to implement.
Transitioning to Low-GWP Alternatives in Unitary Air Conditioning
This fact sheet provides current information on low-Global Warming Potential (GWP) refrigerant alternatives used in unitary air-conditioning equipment, relevant to the Montreal Protocol on Substances that Deplete the Ozone Layer.
Modeling Sampling in Tensor Products of Unitary Invariant Subspaces
Directory of Open Access Journals (Sweden)
Antonio G. García
2016-01-01
Full Text Available The use of unitary invariant subspaces of a Hilbert space H is nowadays a recognized fact in the treatment of sampling problems. Indeed, shift-invariant subspaces of L2(R and also periodic extensions of finite signals are remarkable examples where this occurs. As a consequence, the availability of an abstract unitary sampling theory becomes a useful tool to handle these problems. In this paper we derive a sampling theory for tensor products of unitary invariant subspaces. This allows merging the cases of finitely/infinitely generated unitary invariant subspaces formerly studied in the mathematical literature; it also allows introducing the several variables case. As the involved samples are identified as frame coefficients in suitable tensor product spaces, the relevant mathematical technique is that of frame theory, involving both finite/infinite dimensional cases.
Exact and Approximate Unitary 2-Designs: Constructions and Applications
Dankert, C; Emerson, J; Livine, E; Dankert, Christoph; Cleve, Richard; Emerson, Joseph; Livine, Etera
2006-01-01
We consider an extension of the concept of spherical t-designs to the unitary group in order to develop a unified framework for analyzing the resource requirements of randomized quantum algorithms. We show that certain protocols based on twirling require a unitary 2-design. We describe an efficient construction for an exact unitary 2-design based on the Clifford group, and then develop a method for generating an epsilon-approximate unitary 2-design that requires only O(n log(1/epsilon)) gates, where n is the number of qubits and epsilon is an appropriate measure of precision. These results lead to a protocol with exponential resource savings over existing experimental methods for estimating the characteristic fidelities of physical quantum processes.
The Theory of Unitary Development of Chengdu and Chongqing
Institute of Scientific and Technical Information of China (English)
HuangQing
2005-01-01
Chengdu and Chongqing are two megalopolises with the synthesized economic strength and the strongest urban competitiveness in the entire western region, which have very important positions in the development of western China. Through horizontal contrast of social economic developing level of the two cities, the two cities' economic foundation of unitary development is analyzed from complementary and integrative relationship. Then the policies and measures of economic unitary development of two cities is put forward.
Free Energies and Fluctuations for the Unitary Brownian Motion
Dahlqvist, Antoine
2016-12-01
We show that the Laplace transforms of traces of words in independent unitary Brownian motions converge towards an analytic function on a non trivial disc. These results allow one to study the asymptotic behavior of Wilson loops under the unitary Yang-Mills measure on the plane with a potential. The limiting objects obtained are shown to be characterized by equations analogue to Schwinger-Dyson's ones, named here after Makeenko and Migdal.
Kharga, Digvijay; Inotani, Daisuke; Hanai, Ryo; Ohashi, Yoji
2017-08-01
We theoretically investigate normal-state properties of a gas mixture of single-component bosons and fermions with a hetero-nuclear Feshbach resonance. Including strong hetero-pairing fluctuations associated with the Feshbach resonance, we calculate single-particle density of states, as well as the spectral weight at various interaction strengths. For this purpose, we employ an improved T-matrix approximation (TMA), where the bare Bose Green's function in the non-selfconsistent TMA self-energy is modified so as to satisfy the Hugenholtz-Pines relation at the Bose-Einstein condensation (BEC) temperature TBEC. In the unitary regime at TBEC, we show that hetero-pairing fluctuations couple Fermi atomic excitations with Fermi molecular excitations, as well as with Bose atomic excitations. Although a similar coupling phenomenon by pairing fluctuations is known to give a pseudo-gapped density of states in the unitary regime of a two-component Fermi gas, such a dip structure is found to not appear even in the unitary limit of a Bose-Fermi mixture. It only appears in the strong-coupling regime. Instead, a spectral peak along the molecular dispersion appears in the spectral weight. We also clarify how this coupling phenomenon is seen in the Bose channel. Since a hetero-nuclear Feshbach resonance, as well as the formation of Bose-Fermi molecules, have been realized, our results would be useful for the study of strong-coupling properties of this unique quantum gas.
Implementation of bipartite or remote unitary gates with repeater nodes
Yu, Li; Nemoto, Kae
2016-08-01
We propose some protocols to implement various classes of bipartite unitary operations on two remote parties with the help of repeater nodes in-between. We also present a protocol to implement a single-qubit unitary with parameters determined by a remote party with the help of up to three repeater nodes. It is assumed that the neighboring nodes are connected by noisy photonic channels, and the local gates can be performed quite accurately, while the decoherence of memories is significant. A unitary is often a part of a larger computation or communication task in a quantum network, and to reduce the amount of decoherence in other systems of the network, we focus on the goal of saving the total time for implementing a unitary including the time for entanglement preparation. We review some previously studied protocols that implement bipartite unitaries using local operations and classical communication and prior shared entanglement, and apply them to the situation with repeater nodes without prior entanglement. We find that the protocols using piecewise entanglement between neighboring nodes often require less total time compared to preparing entanglement between the two end nodes first and then performing the previously known protocols. For a generic bipartite unitary, as the number of repeater nodes increases, the total time could approach the time cost for direct signal transfer from one end node to the other. We also prove some lower bounds of the total time when there are a small number of repeater nodes. The application to position-based cryptography is discussed.
Gradient catastrophe and Fermi-edge resonances in Fermi gas.
Bettelheim, E; Kaplan, Y; Wiegmann, P
2011-04-22
Any smooth spatial disturbance of a degenerate Fermi gas inevitably becomes sharp. This phenomenon, called the gradient catastrophe, causes the breakdown of a Fermi sea to multiconnected components characterized by multiple Fermi points. We argue that the gradient catastrophe can be probed through a Fermi-edge singularity measurement. In the regime of the gradient catastrophe the Fermi-edge singularity problem becomes a nonequilibrium and nonstationary phenomenon. We show that the gradient catastrophe transforms the single-peaked Fermi-edge singularity of the tunneling (or absorption) spectrum to a sequence of multiple asymmetric singular resonances. An extension of the bosonic representation of the electronic operator to nonequilibrium states captures the singular behavior of the resonances.
Thermodynamic properties of noninteracting quantum gases with spin-orbit coupling
Energy Technology Data Exchange (ETDEWEB)
He Li [Jiangsu University of Science and Technology, Zhangjiagang, Jiangsu, 215600 (China); Yu Zengqiang [Institute for Advanced Study, Tsinghua University, Beijing, 100084 (China)
2011-08-15
In this brief report we study thermodynamic properties of noninteracting quantum gases with isotropic spin-orbit coupling. At high temperature, coefficients of virial expansion depend on both temperature T and spin-orbit coupling strength {kappa}. For strong coupling, virial expansion is applicable to the temperature region below the conventional degenerate temperature T{sub F}. At low temperature, specific heat is proportional to {radical}(T) in Bose gases and T in Fermi gases. Temperature dependence of the chemical potential of fermions shows a different behavior when the Fermi surface is above and below the Dirac point.
Quantum Simulations of Condensed Matter Systems Using Ultra-Cold Atomic Gases
2013-03-01
Feynman diagrams versus Fermi-‐gas Feynman emulator”, Nature Physics 8, 366...BEC-‐BCS Crossover and the Unitary Fermi Gas”, Lecture Notes in Physics , Volume 836, edited by Wilhelm... Lecture at 100th Anniversary Solvay Conference on Physics , "The Theory of the
Sur, Shouvik; Lee, Sung-Sik
2014-07-01
A non-Fermi liquid state without time-reversal and parity symmetries arises when a chiral Fermi surface is coupled with a soft collective mode in two space dimensions. The full Fermi surface is described by a direct sum of chiral patch theories, which are decoupled from each other in the low-energy limit. Each patch includes low-energy excitations near a set of points on the Fermi surface with a common tangent vector. General patch theories are classified by the local shape of the Fermi surface, the dispersion of the critical boson, and the symmetry group, which form the data for distinct universality classes. We prove that a large class of chiral non-Fermi liquid states exists as stable critical states of matter. For this, we use a renormalization group scheme where low-energy excitations of the Fermi surface are interpreted as a collection of (1+1)-dimensional chiral fermions with a continuous flavor labeling the momentum along the Fermi surface. Due to chirality, the Wilsonian effective action is strictly UV finite. This allows one to extract the exact scaling exponents although the theories flow to strongly interacting field theories at low energies. In general, the low-energy effective theory of the full Fermi surface includes patch theories of more than one universality classes. As a result, physical responses include multiple universal components at low temperatures. We also point out that, in quantum field theories with extended Fermi surface, a noncommutative structure naturally emerges between a coordinate and a momentum which are orthogonal to each other. We show that the invalidity of patch description for Fermi liquid states is tied with the presence of UV/IR mixing associated with the emergent noncommutativity. On the other hand, UV/IR mixing is suppressed in non-Fermi liquid states due to UV insensitivity, and the patch description is valid.
Chen, Jing-Yuan; Son, Dam Thanh
2017-02-01
We develop an extension of the Landau Fermi liquid theory to systems of interacting fermions with non-trivial Berry curvature. We propose a kinetic equation and a constitutive relation for the electromagnetic current that together encode the linear response of such systems to external electromagnetic perturbations, to leading and next-to-leading orders in the expansion over the frequency and wave number of the perturbations. We analyze the Feynman diagrams in a large class of interacting quantum field theories and show that, after summing up all orders in perturbation theory, the current-current correlator exactly matches with the result obtained from the kinetic theory.
Peltier cooling of fermionic quantum gases.
Grenier, Ch; Georges, A; Kollath, C
2014-11-14
We propose a cooling scheme for fermionic quantum gases, based on the principles of the Peltier thermoelectric effect and energy filtering. The system to be cooled is connected to another harmonically trapped gas acting as a reservoir. The cooling is achieved by two simultaneous processes: (i) the system is evaporatively cooled, and (ii) cold fermions from deep below the Fermi surface of the reservoir are injected below the Fermi level of the system, in order to fill the "holes" in the energy distribution. This is achieved by a suitable energy dependence of the transmission coefficient connecting the system to the reservoir. The two processes can be viewed as simultaneous evaporative cooling of particles and holes. We show that both a significantly lower entropy per particle and faster cooling rate can be achieved in this way than by using only evaporative cooling.
Peltier Cooling of Fermionic Quantum Gases
Grenier, Ch.; Georges, A.; Kollath, C.
2014-11-01
We propose a cooling scheme for fermionic quantum gases, based on the principles of the Peltier thermoelectric effect and energy filtering. The system to be cooled is connected to another harmonically trapped gas acting as a reservoir. The cooling is achieved by two simultaneous processes: (i) the system is evaporatively cooled, and (ii) cold fermions from deep below the Fermi surface of the reservoir are injected below the Fermi level of the system, in order to fill the "holes" in the energy distribution. This is achieved by a suitable energy dependence of the transmission coefficient connecting the system to the reservoir. The two processes can be viewed as simultaneous evaporative cooling of particles and holes. We show that both a significantly lower entropy per particle and faster cooling rate can be achieved in this way than by using only evaporative cooling.
New physics of metals: fermi surfaces without Fermi liquids.
Anderson, P W
1995-01-01
I relate the historic successes, and present difficulties, of the renormalized quasiparticle theory of metals ("AGD" or Fermi liquid theory). I then describe the best-understood example of a non-Fermi liquid, the normal metallic state of the cuprate superconductors.
Haldane, F. D. M.
2014-01-01
The role of "Fermi arc" surface-quasiparticle states in "topological metals" (where some Fermi surface sheets have non-zero Chern number) is examined. They act as "Fermi-level plumbing" conduits that transfer quasiparticles among groups of apparently-disconnected Fermi sheets with non-zero Chern numbers to maintain equality of their chemical potentials, which is required by gauge invariance. Fermi arcs have a chiral tangential attachment to the surface projections of sheets of the bulk Fermi ...
Efficient unitary designs with nearly time-independent Hamiltonian dynamics
Nakata, Yoshifumi; Koashi, Masato; Winter, Andreas
2016-01-01
We provide new constructions of unitary $t$-designs for general $t$ on one qudit and $N$ qubits, and propose a design Hamiltonian, a random Hamiltonian of which dynamics always forms a unitary design after a threshold time, as a basic framework to investigate randomising time evolution in quantum many-body systems. The new constructions are based on recently proposed schemes of repeating random unitaires diagonal in mutually unbiased bases. We first show that, if a pair of the bases satisfies a certain condition, the process on one qudit approximately forms a unitary $t$-design after $O(t)$ repetitions. We then construct quantum circuits on $N$ qubits that achieve unitary $t$-designs for $t = o(N^{1/2})$ using $O(t N^2)$ gates, improving the previous result using $O(t^{10}N^2)$ gates in terms of $t$. Based on these results, we present a design Hamiltonian with periodically changing two-local spin-glass-type interactions, leading to fast and relatively natural realisations of unitary designs in complex many-bo...
Fermi Communications and Public Outreach
Cominsky, L
2015-01-01
The Sonoma State University (SSU) Education and Public Outreach (E/PO) group participates in the planning and execution of press conferences that feature noteworthy Fermi discoveries, as well as supporting social media and outreach websites. We have also created many scientific illustrations for the media, tools for amateur astronomers for use at star parties, and have given numerous public talks about Fermi discoveries.
This FERMI multi-chip module contains five million transistors. 25 000 of these modules will handle the flood of information through parts of the ATLAS and CMS detectors at the LHC. To select interesting events for recording, crucial decisions are taken before the data leaves the detector. FERMI modules are being developed at CERN in partnership with European industry.
Mechanics of gases; Mechanik der Gase
Energy Technology Data Exchange (ETDEWEB)
Richter, Dieter [Helmholtz-Zentrum Berlin fuer Materialien und Energie, Berlin (Germany). BESSY II
2010-07-01
Compact synopsis for natural scientists, engineers and vacuum specialists. Application-oriented presentation with many practical examples and exercises. Ideal for bachelor study programmes. Knowledge on the movement, speed and energy of gas particles are an important prerequisite for an understanding of modern technologies such as vacuum engineering, or, closely related to the former, of vacuum physics or the handling of gases. This book presents the mechanics of gases in a readily understandable manner. The mathematics used is no more complex than necessary. The material is presented in coherent manner and follows a logical progression. The book begins with a description of Maxwell's velocity distribution. This is followed by a derivation of the equations of state for ideal gases as well as a description of the most important equations of state for real gases. Next the author derives relationships for all important gas kinetic parameters and shows how they can be determined experimentally. The presentation ends with explanations of selected calculations and a synopsis of all important formulas. The book contains a number of examples which are oriented towards questions as they arise in engineering or applied physics. The content level is ''Upper Undergraduate''. Keywords: gas dynamics; gas kinetics; ideal and real gas; kinetic gases; textbook of gas dynamics; textbook of gas kinetics; textbook of gas mechanics; Maxwell's law; gas mechanics; fluid mechanics; equations of state for gases. [German] - Kompakte Zusammenfassung fuer Naturwissenschaftler, Ingenieure und Vakuumspezialisten. - Anwendungsorientierte Praesentation mit vielen Praxisbeispielen und Aufgaben. - Ideal fuer das Bachelor-Studium Kenntnisse ueber die Bewegung von Gasteilchen, deren Geschwindigkeit und Energie sind eine wichtige Voraussetzung zum Verstaendnis moderner Technologien, z. B. der Vakuumtechnik, und eng damit verknuepft der Vakuumphysik oder der Handhabung von
Bloch-Messiah reduction of Gaussian unitaries by Takagi factorization
Cariolaro, Gianfranco; Pierobon, Gianfranco
2016-12-01
The Bloch-Messiah (BM) reduction allows the decomposition of an arbitrarily complicated Gaussian unitary into a very simple scheme in which linear optical components are separated from nonlinear ones. The nonlinear part is due to the squeezing possibly present in the Gaussian unitary. The reduction is usually obtained by exploiting the singular value decomposition (SVD) of the matrices appearing in the Bogoliubov transformation of the given Gaussian unitary. This paper discusses a different approach, where the BM reduction is obtained in a straightforward way. It is based on the Takagi factorization of the (complex and symmetric) squeeze matrix and has the advantage of avoiding several matrix operations of the previous approach (polar decomposition, eigendecomposition, SVD, and Takagi factorization). The theory is illustrated with an application example in which the previous and present approaches are compared.
Defect of a Kronecker product of unitary matrices
Tadej, Wojciech
2010-01-01
The defect d(U) of an NxN unitary matrix U with no zero entries is the dimension (called the generalized defect D(U)) of the real space of directions, moving into which from U we do not disturb the moduli |U_ij| as well as the Gram matrix U'*U in the first order, diminished by 2N-1. Calculation of d(U) involves calculating the dimension of the space in R^(N^2) spanned by a certain set of vectors associated with U. We split this space into a direct sum, assuming that U is a Kronecker product of unitary matrices, thus making it easier to perform calculations numerically. Basing on this, we give a lower bound on D(U) (equivalently d(U)), supposing it is achieved for most unitaries with a fixed Kronecker product structure. Also supermultiplicativity of D(U) with respect to Kronecker subproducts of U is shown.
Compressor-fan unitary structure for air conditioning system
Dreiman, N.
2015-08-01
An extremely compact, therefore space saving unitary structure of short axial length is produced by radial integration of a revolving piston rotary compressor and an impeller of a centrifugal fan. The unitary structure employs single motor to run as the compressor so the airflow fan and eliminates duality of motors, related power supply and control elements. Novel revolving piston rotary compressor which provides possibility for such integration comprises the following: a suction gas delivery system which provides cooling of the motor and supplies refrigerant into the suction chamber under higher pressure (supercharged); a modified discharge system and lubricating oil supply system. Axial passages formed in the stationary crankshaft are used to supply discharge gas to a condenser, to return vaporized cooling agent from the evaporator to the suction cavity of the compressor, to pass a lubricant and to accommodate wiring supplying power to the unitary structure driver -external rotor electric motor.
Amending entanglement-breaking channels via intermediate unitary operations
Cuevas, Á.; De Pasquale, A.; Mari, A.; Orieux, A.; Duranti, S.; Massaro, M.; Di Carli, A.; Roccia, E.; Ferraz, J.; Sciarrino, F.; Mataloni, P.; Giovannetti, V.
2017-08-01
We report a bulk optics experiment demonstrating the possibility of restoring the entanglement distribution through noisy quantum channels by inserting a suitable unitary operation (filter) in the middle of the transmission process. We focus on two relevant classes of single-qubit channels consisting in repeated applications of rotated phase-damping or rotated amplitude-damping maps, both modeling the combined Hamiltonian and dissipative dynamics of the polarization state of single photons. Our results show that interposing a unitary filter between two noisy channels can significantly improve entanglement transmission. This proof-of-principle demonstration could be generalized to many other physical scenarios where entanglement-breaking communication lines may be amended by unitary filters.
Non-unitary fusion categories and their doubles via endomorphisms
Evans, David E
2015-01-01
We realise non-unitary fusion categories using subfactor-like methods, and compute their quantum doubles and modular data. For concreteness we focus on generalising the Haagerup-Izumi family of Q-systems. For example, we construct endomorphism realisations of the (non-unitary) Yang-Lee model, and non-unitary analogues of one of the even subsystems of the Haagerup subfactor and of the Grossman-Snyder system. We supplement Izumi's equations for identifying the half-braidings, which were incomplete even in his Q-system setting. We conjecture a remarkably simple form for the modular S and T matrices of the doubles of these fusion categories. We would expect all of these doubles to be realised as the category of modules of a rational VOA and conformal net of factors. We expect our approach will also suffice to realise the non-semisimple tensor categories arising in logarithmic conformal field theories.
Time reversal and exchange symmetries of unitary gate capacities
Harrow, A W; Harrow, Aram W.; Shor, Peter W.
2005-01-01
Unitary gates are an interesting resource for quantum communication in part because they are always invertible and are intrinsically bidirectional. This paper explores these two symmetries: time-reversal and exchange of Alice and Bob. We will present examples of unitary gates that exhibit dramatic separations between forward and backward capacities (even when the back communication is assisted by free entanglement) and between entanglement-assisted and unassisted capacities, among many others. Along the way, we will give a general time-reversal rule for relating the capacities of a unitary gate and its inverse that will explain why previous attempts at finding asymmetric capacities failed. Finally, we will see how the ability to erase quantum information and destroy entanglement can be a valuable resource for quantum communication.
Enrico Fermi Symposium at CERN : opening celebration
CERN. Geneva. Audiovisual Unit
2002-01-01
You are cordially invited to the opening celebration on Thursday 12 September at 16:00 (Main Building, Council Chamber), which will include speechs from: Luciano Maiani - Welcome and Introduction Antonino Zichichi - The New 'Centro Enrico Fermi' at Via Panisperna Ugo Amaldi - Fermi at Via Panisperna and the birth of Nuclear Medicine Jack Steinberger - Fermi in Chicago Valentin Telegdi - A Close-up of Fermi Arnaldo Stefanini - Celebrating Fermi's Centenary in Documents and Pictures and the screening of a documentary video about Fermi: Scienziati a Pisa: Enrico Fermi (Scientists at Pisa: Enrico Fermi) created by Francesco Andreotti for La Limonaia from early film, photographs and sound recordings (English version - c. 30 mins).
Directory of Open Access Journals (Sweden)
Akihito Soeda
2010-06-01
Full Text Available We study how two pieces of localized quantum information can be delocalized across a composite Hilbert space when a global unitary operation is applied. We classify the delocalization power of global unitary operations on quantum information by investigating the possibility of relocalizing one piece of the quantum information without using any global quantum resource. We show that one-piece relocalization is possible if and only if the global unitary operation is local unitary equivalent of a controlled-unitary operation. The delocalization power turns out to reveal different aspect of the non-local properties of global unitary operations characterized by their entangling power.
Potential Energy Surfaces Using Algebraic Methods Based on Unitary Groups
Directory of Open Access Journals (Sweden)
Renato Lemus
2011-01-01
Full Text Available This contribution reviews the recent advances to estimate the potential energy surfaces through algebraic methods based on the unitary groups used to describe the molecular vibrational degrees of freedom. The basic idea is to introduce the unitary group approach in the context of the traditional approach, where the Hamiltonian is expanded in terms of coordinates and momenta. In the presentation of this paper, several representative molecular systems that permit to illustrate both the different algebraic approaches as well as the usual problems encountered in the vibrational description in terms of internal coordinates are presented. Methods based on coherent states are also discussed.
A construction of fully diverse unitary space-time codes
Institute of Scientific and Technical Information of China (English)
YU Fei; TONG HongXi
2009-01-01
Fully diverse unitary space-time codes are useful in multiantenna communications,especially in multiantenna differential modulation.Recently,two constructions of parametric fully diverse unitary space-time codes for three antennas system have been introduced.We propose a new construction method based on the constructions.In the present paper,fully diverse codes for systems of odd prime number antennas are obtained from this construction.Space-time codes from present construction are found to have better error performance than many best known ones.
Non-unitary probabilistic quantum computing circuit and method
Williams, Colin P. (Inventor); Gingrich, Robert M. (Inventor)
2009-01-01
A quantum circuit performing quantum computation in a quantum computer. A chosen transformation of an initial n-qubit state is probabilistically obtained. The circuit comprises a unitary quantum operator obtained from a non-unitary quantum operator, operating on an n-qubit state and an ancilla state. When operation on the ancilla state provides a success condition, computation is stopped. When operation on the ancilla state provides a failure condition, computation is performed again on the ancilla state and the n-qubit state obtained in the previous computation, until a success condition is obtained.
A construction of fully diverse unitary space-time codes
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
Fully diverse unitary space-time codes are useful in multiantenna communications, especially in multiantenna differential modulation. Recently, two constructions of parametric fully diverse unitary space-time codes for three antennas system have been introduced. We propose a new construction method based on the constructions. In the present paper, fully diverse codes for systems of odd prime number antennas are obtained from this construction. Space-time codes from present construction are found to have better error performance than many best known ones.
Pattern, participation, praxis, and power in unitary appreciative inquiry.
Cowling, W Richard
2004-01-01
This article is an explication and clarification of unitary appreciative inquiry based on several recent projects. Four central dimensions of the inquiry process are presented: pattern, participation, praxis, and power. Examples of inquiry projects demonstrate and illuminate the possibilities of unitary appreciative inquiry. The relationship of these central dimensions to experiential, presentational, propositional, and practical knowledge outcomes is articulated. A matrix framework integrating pattern, participation, praxis, and power demonstrates the potential for generating knowledge relevant to the lives of participants and creating an inquiry process worthy of human aspiration.
Tables of the principal unitary representations of Fedorov groups
Faddeyev, D K
1961-01-01
Tables of the Principal Unitary Representations of Fedorov Groups contains tables of all the principal representations of Fedorov groups from which all irreducible unitary representations can be obtained with the help of some standard operations. The work originated at a seminar on mathematical crystallography held in 1952-1953 at the Faculty of Mathematics and Mechanics of the Leningrad State University. The book is divided into two parts. The first part discusses the relation between the theory of representations and the generalized Fedorov groups in Shubnikov's sense. It shows that all un
Directory of Open Access Journals (Sweden)
Ynduráin, Francisco J.
2002-01-01
Full Text Available Not available
Los azares de las onomásticas hacen coincidir en este año el centenario del nacimiento de tres de los más grandes físicos del siglo XX. Dos de ellos, Fermi y Heisenberg, dejaron una marca fundamental en la ciencia (ambos, pero sobre todo el segundo y, el primero, también en la tecnología. Lawrence, indudablemente de un nivel inferior al de los otros dos, estuvo sin embargo en el origen de uno de los desarrollos tecnológicos que han sido básicos para la exploración del universo subnuclear en la segunda mitad del siglo que ha terminado hace poco, el de los aceleradores de partículas.
Phase correlations and quasicondensate in a two-dimensional ultracold Fermi gas
Energy Technology Data Exchange (ETDEWEB)
Tempere, J., E-mail: jacques.tempere@uantwerpen.be [Theory of Quantum and Complex Systems, Universiteit Antwerpen, Universiteitsplein 1, B-2610 Antwerpen (Belgium); Lyman Laboratory of Physics, Harvard University, Cambridge, MA 02138 (United States); Klimin, S.N. [Theory of Quantum and Complex Systems, Universiteit Antwerpen, Universiteitsplein 1, B-2610 Antwerpen (Belgium)
2015-02-15
The interplay between dimensionality, coherence and interaction in superfluid Fermi gases is analyzed by the phase correlation function of the field of fermionic pairs. We calculate this phase correlation function for a two-dimensional superfluid Fermi gas with s-wave interactions within the Gaussian pair fluctuation formalism. The spatial behavior of the correlation function is shown to exhibit a rapid (exponential) decay at short distances and a characteristic algebraic decay at large distances, with an exponent matching that expected from the Berezinskii–Kosterlitz–Thouless theory of 2D Bose superfluids. We conclude that the Gaussian pair fluctuation approximation is able to capture the physics of quasi-long-range order in two-dimensional Fermi gases. - Highlights: • The phase correlation functions for an ultracold Fermi gas in 2D are calculated. • The decay of the correlation functions is algebraic at long distances. • The Gaussian pair fluctuation approach is shown to capture the quasicondensate physics in 2D Fermi gases.
Sur, Shouvik; Lee, Sung-Sik
2016-11-01
We study non-Fermi-liquid states that arise at the quantum critical points associated with the spin density wave (SDW) and charge density wave (CDW) transitions in metals with twofold rotational symmetry. We use the dimensional regularization scheme, where a one-dimensional Fermi surface is embedded in (3 -ɛ ) -dimensional momentum space. In three dimensions, quasilocal marginal Fermi liquids arise both at the SDW and CDW critical points: the speed of the collective mode along the ordering wave vector is logarithmically renormalized to zero compared to that of Fermi velocity. Below three dimensions, however, the SDW and CDW critical points exhibit drastically different behaviors. At the SDW critical point, a stable anisotropic non-Fermi-liquid state is realized for small ɛ , where not only time but also different spatial coordinates develop distinct anomalous dimensions. The non-Fermi liquid exhibits an emergent algebraic nesting as the patches of Fermi surface are deformed into a universal power-law shape near the hot spots. Due to the anisotropic scaling, the energy of incoherent spin fluctuations disperse with different power laws in different momentum directions. At the CDW critical point, on the other hand, the perturbative expansion breaks down immediately below three dimensions as the interaction renormalizes the speed of charge fluctuations to zero within a finite renormalization group scale through a two-loop effect. The difference originates from the fact that the vertex correction antiscreens the coupling at the SDW critical point whereas it screens at the CDW critical point.
An interpolatory ansatz captures the physics of one-dimensional confined Fermi systems
DEFF Research Database (Denmark)
Andersen, Molte Emil Strange; Salami Dehkharghani, Amin; Volosniev, A. G.;
2016-01-01
beyond the Bethe ansatz and bosonisation allow us to predict the behaviour of one-dimensional confined systems with strong short-range interactions, and new experiments with cold atomic Fermi gases have already confirmed these theories. Here we demonstrate that a simple linear combination of the strongly...
Metastability and coherence of repulsive polarons in a strongly interacting Fermi mixture
DEFF Research Database (Denmark)
Kohstall, Cristoph; Zaccanti, Mattheo; Jag, Matthias;
2012-01-01
Ultracold Fermi gases with tunable interactions provide a test bed for exploring the many-body physics of strongly interacting quantum systems1, 2, 3, 4. Over the past decade, experiments have investigated many intriguing phenomena, and precise measurements of ground-state properties have provided...... benchmarks for the development of theoretical descriptions. Metastable states in Fermi gases with strong repulsive interactions5, 6, 7, 8, 9, 10, 11 represent an exciting area of development. The realization of such systems is challenging, because a strong repulsive interaction in an atomic quantum gas...... implies the existence of a weakly bound molecular state, which makes the system intrinsically unstable against decay. Here we use radio-frequency spectroscopy to measure the complete excitation spectrum of fermionic 40K impurities resonantly interacting with a Fermi sea of 6Li atoms. In particular, we...
Two-Element Generation of Unitary Groups Over Finite Fields
2013-01-31
like to praise my Lord and Savior, Jesus Christ , for allowing me this opportunity to work on a Ph.D in mathematics, and for His sustaining grace...Ishibashi’s original result. The paper’s main theorem will show that all unitary groups over finite fields of odd characteristic are generated by only two
Experimental Realization of Perfect Discrimination for Two Unitary Operations
Institute of Scientific and Technical Information of China (English)
LIU Jian-Jun; HONG Zhi
2008-01-01
We experimentally demonstrate perfect discrimination between two unitary operations by using the sequential scheme proposed by Duan et al.[Phys. Rev. Lett. 98 (2007) 100503] Also, we show how to understand the scheme and to calculate the parameters for two-dimensional operations in the picture of the Bloch sphere.
Unitary operator bases and q-deformed algebras
Energy Technology Data Exchange (ETDEWEB)
Galleti, D.; Lunardi, J.T.; Pimentel, B.M. [Instituto de Fisica Teorica (IFT), Sao Paulo, SP (Brazil); Lima, C.L. [Sao Paulo Univ., SP (Brazil). Inst. de Fisica
1995-11-01
Starting from the Schwinger unitary operator bases formalism constructed out of a finite dimensional state space, the well-know q-deformed communication relation is shown to emergence in a natural way, when the deformation parameter is a root of unity. (author). 14 refs.
Unitary operator bases and Q-deformed algebras
Energy Technology Data Exchange (ETDEWEB)
Galetti, D.; Pimentel, B.M. [Instituto de Fisica Teorica (IFT), Sao Paulo, SP (Brazil); Lima, C.L. [Sao Paulo Univ., SP (Brazil). Inst. de Fisica. Grupo de Fisica Nuclear e Teorica e Fenomenologia de Particulas Elementares; Lunardi, J.T. [Universidade Estadual de Ponta Grossa, PR (Brazil). Dept. de Matematica e Estatistica
1998-03-01
Starting from the Schwinger unitary operator bases formalism constructed out of a finite dimensional state space, the well-know q-deformed commutation relation is shown to emerge in a natural way, when the deformation parameter is a root of unity. (author)
The Wilson loop in the Gaussian Unitary Ensemble
Gurau, Razvan
2016-01-01
Using the supersymmetric formalism we compute exactly at finite $N$ the expectation of the Wilson loop in the Gaussian Unitary Ensemble and derive an exact formula for the spectral density at finite $N$. We obtain the same result by a second method relying on enumerative combinatorics and show that it leads to a novel proof of the Harer-Zagier series formula.
An algebraic study of unitary one dimensional quantum cellular automata
Arrighi, P
2005-01-01
We provide algebraic characterizations of unitary one dimensional quantum cellular automata. We do so both by algebraizing existing decision procedures, and by adding constraints into the model which do not change the quantum cellular automata's computational power. The configurations we consider have finite but unbounded size.
CONSTRUCTION OF AUTHENTICATION CODES WITH ARBITRATION FROM UNITARY GEOMETRY
Institute of Scientific and Technical Information of China (English)
LiRuihu; OuoLuobin
1999-01-01
A family of authentication codes with arbitration is constructed from unitary geome-try,the parameters and the probabilities of deceptions of the codes are also computed. In a spe-cial case a perfect authentication code with arbitration is ohtalned.
Establishing the Unitary Classroom: Organizational Change and School Culture.
Eddy, Elizabeth M.; True, Joan H.
1980-01-01
This paper examines the organizational changes introduced in two elementary schools to create unitary (desegregated) classrooms. The different models adopted by the two schools--departmentalization and team teaching--are considered as expressions of their patterns of interaction, behavior, and values. (Part of a theme issue on educational…
Linear programming bounds for unitary space time codes
Creignou, Jean
2008-01-01
The linear programming method is applied to the space $\\U_n(\\C)$ of unitary matrices in order to obtain bounds for codes relative to the diversity sum and the diversity product. Theoretical and numerical results improving previously known bounds are derived.
The fermi paradox is neither Fermi's nor a paradox.
Gray, Robert H
2015-03-01
The so-called Fermi paradox claims that if technological life existed anywhere else, we would see evidence of its visits to Earth--and since we do not, such life does not exist, or some special explanation is needed. Enrico Fermi, however, never published anything on this topic. On the one occasion he is known to have mentioned it, he asked "Where is everybody?"--apparently suggesting that we do not see extraterrestrials on Earth because interstellar travel may not be feasible, but not suggesting that intelligent extraterrestrial life does not exist or suggesting its absence is paradoxical. The claim "they are not here; therefore they do not exist" was first published by Michael Hart, claiming that interstellar travel and colonization of the Galaxy would be inevitable if intelligent extraterrestrial life existed, and taking its absence here as proof that it does not exist anywhere. The Fermi paradox appears to originate in Hart's argument, not Fermi's question. Clarifying the origin of these ideas is important, because the Fermi paradox is seen by some as an authoritative objection to searching for evidence of extraterrestrial intelligence--cited in the U.S. Congress as a reason for killing NASA's SETI program on one occasion. But evidence indicates that it misrepresents Fermi's views, misappropriates his authority, deprives the actual authors of credit, and is not a valid paradox.
Quantum gases finite temperature and non-equilibrium dynamics
Szymanska, Marzena; Davis, Matthew; Gardiner, Simon
2013-01-01
The 1995 observation of Bose-Einstein condensation in dilute atomic vapours spawned the field of ultracold, degenerate quantum gases. Unprecedented developments in experimental design and precision control have led to quantum gases becoming the preferred playground for designer quantum many-body systems. This self-contained volume provides a broad overview of the principal theoretical techniques applied to non-equilibrium and finite temperature quantum gases. Covering Bose-Einstein condensates, degenerate Fermi gases, and the more recently realised exciton-polariton condensates, it fills a gap by linking between different methods with origins in condensed matter physics, quantum field theory, quantum optics, atomic physics, and statistical mechanics. Thematically organised chapters on different methodologies, contributed by key researchers using a unified notation, provide the first integrated view of the relative merits of individual approaches, aided by pertinent introductory chapters and the guidance of ed...
Kinetic equation for strongly interacting dense Fermi systems
Lipavsky, P; Spicka, V
2001-01-01
We review the non-relativistic Green's-function approach to the kinetic equations for Fermi liquids far from equilibrium. The emphasis is on the consistent treatment of the off-shell motion between collisions and on the non-instant and non-local picture of binary collisions. The resulting kinetic equation is of the Boltzmann type, and it represents an interpolation between the theory of transport in metals and the theory of moderately dense gases. The free motion of particles is renormalised by various mean field and mass corrections in the spirit of Landau's quasiparticles in metals. The collisions are non-local in the spirit of Enskog's theory of non-ideal gases. The collisions are moreover non-instant, a feature which is absent in the theory of gases, but which is shown to be important for dense Fermi systems. In spite of its formal complexity, the presented theory has a simple implementation within the Monte-Carlo simulation schemes. Applications in nuclear physics are given for heavy-ion reactions and th...
Enrico Fermi the obedient genius
Bruzzaniti, Giuseppe
2016-01-01
This biography explores the life and career of the Italian physicist Enrico Fermi, which is also the story of thirty years that transformed physics and forever changed our understanding of matter and the universe: nuclear physics and elementary particle physics were born, nuclear fission was discovered, the Manhattan Project was developed, the atomic bombs were dropped, and the era of “big science” began. It would be impossible to capture the full essence of this revolutionary period without first understanding Fermi, without whom it would not have been possible. Enrico Fermi: The Obedient Genius attempts to shed light on all aspects of Fermi’s life - his work, motivation, influences, achievements, and personal thoughts - beginning with the publication of his first paper in 1921 through his death in 1954. During this time, Fermi demonstrated that he was indeed following in the footsteps of Galileo, excelling in his work both theoretically and experimentally by deepening our understanding of the Pauli e...
Caraveo, Patrizia A
2010-01-01
2009 has been an extraordinary year for gamma-ray pulsar astronomy and 2010 promises to be equally good. Not only have we registered an extraordinary increase in the number of pulsars detected in gamma rays, but we have also witnessed the birth of new sub-families: first of all, the radio-quiet gamma pulsars and later an ever growing number of millisecond pulsars, a real surprise. We started with a sample of 7 gamma-ray emitting neutron stars (6 radio pulsars and Geminga) and now the Fermi-LAT harvest encompasses 24 "Geminga-like" new gamma-ray pulsars, a dozen millisecond pulsars and about thirty radio pulsars. Moreover, radio searches targeted to LAT unidentified sources yielded 18 new radio millisecond pulsars, several of which have been already detected also in gamma rays. Thus, currently the family of gamma-ray emitting neutron stars seems to be evenly divided between classical radio pulsars, millisecond pulsars and radio quiet neutron stars.
Instability of Non-Fermi Liquid Behavior in the Two-Channel Kondo Model
Institute of Scientific and Technical Information of China (English)
YUAN Qing-Shan; CHEN Hong; ZHANG Yu-Mei
2001-01-01
The effects of interchannel scattering of conduction electrons by the impu rity and repulsion of conduction electrons at the impurity site on the two-channel Kondo model are simultaneously considered in this paper.It is shown that these two perturbations will substantially modify the usual local non-Fermi liquid behavior of the two-channel Kondo model.With bosonization and unitary transformations we find that the system can be transformed into a single channel Kondo model with anisotropy between longitudinal and transverse exchange couplings.Whatever for originally antiferromagnetic or ferromagnetic isotropic coupling,the system always flows to strong-coupling limit,which exhibits local Fermi liquid behavior at low temperatures.
Tomkins, RPT
1991-01-01
This volume contains tabulated collections and critical evaluations of original data for the solubility of gases in molten salts, gathered from chemical literature through to the end of 1989. Within the volume, material is arranged according to the individual gas. The gases include hydrogen halides, inert gases, oxygen, nitrogen, hydrogen, carbon dioxide, water vapor and halogens. The molten salts consist of single salts, binary mixtures and multicomponent systems. Included also, is a special section on the solubility of gases in molten silicate systems, focussing on slags and fluxes.
Schoen, Helmut
2015-01-01
Technical gases are used in almost every field of industry, science and medicine and also as a means of control by government authorities and institutions and are regarded as indispensable means of assistance. In this complete handbook of purified gases the physical foundations of purified gases and mixtures as well as their manufacturing, purification, analysis, storage, handling and transport are presented in a comprehensive way. This important reference work is accompanied with a large number of Data Sheets dedicated to the most important purified gases.
Large Representation Recurrences in Large N Random Unitary Matrix Models
Karczmarek, Joanna L
2011-01-01
In a random unitary matrix model at large N, we study the properties of the expectation value of the character of the unitary matrix in the rank k symmetric tensor representation. We address the problem of whether the standard semiclassical technique for solving the model in the large N limit can be applied when the representation is very large, with k of order N. We find that the eigenvalues do indeed localize on an extremum of the effective potential; however, for finite but sufficiently large k/N, it is not possible to replace the discrete eigenvalue density with a continuous one. Nonetheless, the expectation value of the character has a well-defined large N limit, and when the discreteness of the eigenvalues is properly accounted for, it shows an intriguing approximate periodicity as a function of k/N.
Efimov-driven phase transitions of the unitary Bose gas.
Piatecki, Swann; Krauth, Werner
2014-03-20
Initially predicted in nuclear physics, Efimov trimers are bound configurations of three quantum particles that fall apart when any one of them is removed. They open a window into a rich quantum world that has become the focus of intense experimental and theoretical research, as the region of 'unitary' interactions, where Efimov trimers form, is now accessible in cold-atom experiments. Here we use a path-integral Monte Carlo algorithm backed up by theoretical arguments to show that unitary bosons undergo a first-order phase transition from a normal gas to a superfluid Efimov liquid, bound by the same effects as Efimov trimers. A triple point separates these two phases and another superfluid phase, the conventional Bose-Einstein condensate, whose coexistence line with the Efimov liquid ends in a critical point. We discuss the prospects of observing the proposed phase transitions in cold-atom systems.
Universal unitary gate for single-photon spinorbit ququart states
Slussarenko, Sergei; Piccirillo, Bruno; Marrucci, Lorenzo; Santamato, Enrico
2009-01-01
The recently demonstrated possibility of entangling opposite values of the orbital angular momentum (OAM) of a photon with its spin enables the realization of nontrivial one-photon spinorbit ququart states, i.e., four-dimensional photon states for quantum information purposes. Hitherto, however, an optical device able to perform arbitrary unitary transformations on such spinorbit photon states has not been proposed yet. In this work we show how to realize such a ``universal unitary gate'' device, based only on existing optical technology, and describe its operation. Besides the quantum information field, the proposed device may find applications wherever an efficient and convenient manipulation of the combined OAM and spin of light is required.
On an average over the Gaussian Unitary Ensemble
Mezzadri, F
2009-01-01
We study the asymptotic limit for large matrix dimension N of the partition function of the unitary ensemble with weight exp(-z^2/2x^2 + t/x - x^2/2). We compute the leading order term of the partition function and of the coefficients of its Taylor expansion. Our results are valid in the range N^(-1/2) < z < N^(1/4). Such partition function contains all the information on a new statistics of the eigenvalues of matrices in the Gaussian Unitary Ensemble (GUE) that was introduced by Berry and Shukla (J. Phys. A: Math. Theor., Vol. 41 (2008), 385202, arXiv:0807.3474). It can also be interpreted as the moment generating function of a singular linear statistics.
Random unitary evolution model of quantum Darwinism with pure decoherence
Balanesković, Nenad
2015-10-01
We study the behavior of Quantum Darwinism [W.H. Zurek, Nat. Phys. 5, 181 (2009)] within the iterative, random unitary operations qubit-model of pure decoherence [J. Novotný, G. Alber, I. Jex, New J. Phys. 13, 053052 (2011)]. We conclude that Quantum Darwinism, which describes the quantum mechanical evolution of an open system S from the point of view of its environment E, is not a generic phenomenon, but depends on the specific form of input states and on the type of S- E-interactions. Furthermore, we show that within the random unitary model the concept of Quantum Darwinism enables one to explicitly construct and specify artificial input states of environment E that allow to store information about an open system S of interest with maximal efficiency.
All unitary cubic curvature gravities in D dimensions
Energy Technology Data Exchange (ETDEWEB)
Sisman, Tahsin Cagri; Guellue, Ibrahim; Tekin, Bayram, E-mail: sisman@metu.edu.tr, E-mail: e075555@metu.edu.tr, E-mail: btekin@metu.edu.tr [Department of Physics, Middle East Technical University, 06531 Ankara (Turkey)
2011-10-07
We construct all the unitary cubic curvature gravity theories built on the contractions of the Riemann tensor in D-dimensional (anti)-de Sitter spacetimes. Our construction is based on finding the equivalent quadratic action for the general cubic curvature theory and imposing ghost and tachyon freedom, which greatly simplifies the highly complicated problem of finding the propagator of cubic curvature theories in constant curvature backgrounds. To carry out the procedure we have also classified all the unitary quadratic models. We use our general results to study the recently found cubic curvature theories using different techniques and the string generated cubic curvature gravity model. We also study the scattering in critical gravity and give its cubic curvature extensions.
Unitary Noise and the Mermin-GHZ Game
Fialík, Ivan
2010-01-01
Communication complexity is an area of classical computer science which studies how much communication is necessary to solve various distributed computational problems. Quantum information processing can be used to reduce the amount of communication required to carry out some distributed problems. We speak of pseudo-telepathy when it is able to completely eliminate the need for communication. Since it is generally very hard to perfectly implement a quantum winning strategy for a pseudo-telepathy game, quantum players are almost certain to make errors even though they use a winning strategy. After introducing a model for pseudo-telepathy games, we investigate the impact of erroneously performed unitary transformations on the quantum winning strategy for the Mermin-GHZ game. The question of how strong the unitary noise can be so that quantum players would still be better than classical ones is also dealt with.
Unitary Noise and the Mermin-GHZ Game
Institute of Scientific and Technical Information of China (English)
Ivan Fialík
2011-01-01
Communication complexity is an area of classical computer science which studies how much communication is necessary to solve various distributed computational problems. Quantum information processing can be used to reduce the amount of communication required to carry out some distributed problems. We speak of pseudo-telepathy when it is able to completely eliminate the need for communication. Since it is generally very hard to perfectly implement a quantum winning strategy for a pseudo-telepathy game, quantum players are almost certain to make errors even though they use a winning strategy. After introducing a model for pseudo-telepathy games, we investigate the impact of erroneously performed unitary transformations on the quantum winning strategy for the Mermin-GHZ game. The question of how strong the unitary noise can be so that quantum players would still be better than classical ones is also dealt with.
Unitary Noise and the Mermin-GHZ Game
Directory of Open Access Journals (Sweden)
Ivan Fialík
2010-06-01
Full Text Available Communication complexity is an area of classical computer science which studies how much communication is necessary to solve various distributed computational problems. Quantum information processing can be used to reduce the amount of communication required to carry out some distributed problems. We speak of pseudo-telepathy when it is able to completely eliminate the need for communication. Since it is generally very hard to perfectly implement a quantum winning strategy for a pseudo-telepathy game, quantum players are almost certain to make errors even though they use a winning strategy. After introducing a model for pseudo-telepathy games, we investigate the impact of erroneously performed unitary transformations on the quantum winning strategy for the Mermin-GHZ game. The question of how strong the unitary noise can be so that quantum players would still be better than classical ones is also dealt with.
Derandomizing Quantum Circuits with Measurement-Based Unitary Designs
Turner, Peter S.; Markham, Damian
2016-05-01
Entangled multipartite states are resources for universal quantum computation, but they can also give rise to ensembles of unitary transformations, a topic usually studied in the context of random quantum circuits. Using several graph state techniques, we show that these resources can "derandomize" circuit results by sampling the same kinds of ensembles quantum mechanically, analogously to a quantum random number generator. Furthermore, we find simple examples that give rise to new ensembles whose statistical moments exactly match those of the uniformly random distribution over all unitaries up to order t , while foregoing adaptive feedforward entirely. Such ensembles—known as t designs—often cannot be distinguished from the "truly" random ensemble, and so they find use in many applications that require this implied notion of pseudorandomness.
ROTATION CONSTELLATION FOR DIFFERENTIAL UNITARY SPACE-TIME MODULATION
Institute of Scientific and Technical Information of China (English)
Li Jun; Cao Haiyan; Wei Gang
2006-01-01
A new constellation which is the multiplication of the rotation matrix and the diagonal matrix according to the number of transmitters is proposed to increase the diversity product, the key property to the performance of the differential unitary space-time modulation. Analyses and the simulation results show that the proposed constellation performs better and 2dB or more coding gain can be achieved over the traditional cyclic constellation.
Unitary-matrix models as exactly solvable string theories
Periwal, Vipul; Shevitz, Danny
1990-01-01
Exact differential equations are presently found for the scaling functions of models of unitary matrices which are solved in a double-scaling limit, using orthogonal polynomials on a circle. For the case of the simplest, k = 1 model, the Painleve II equation with constant 0 is obtained; possible nonperturbative phase transitions exist for these models. Equations are presented for k = 2 and 3, and discussed with a view to asymptotic behavior.
Unitary transformation method for solving generalized Jaynes-Cummings models
Indian Academy of Sciences (India)
Sudha Singh
2006-03-01
Two fully quantized generalized Jaynes-Cummings models for the interaction of a two-level atom with radiation field are treated, one involving intensity dependent coupling and the other involving multiphoton interaction between the field and the atom. The unitary transformation method presented here not only solves the time dependent problem but also allows a determination of the eigensolutions of the interacting Hamiltonian at the same time.
Unitary representations of the fundamental group of orbifolds
Indian Academy of Sciences (India)
INDRANIL BISWAS; AMIT HOGADI
2016-10-01
Let $X$ be a smooth complex projective variety of dimension $n$ and $\\mathcal{L}$ an ample line bundle on it. There is a well known bijective correspondence between the isomorphism classes of polystable vector bundles $E$ on $X$ with $c_{1}(E) = 0 = c_{2}(E) \\cdot c_{1} \\mathcal (L)^{n−2}$ and the equivalence classes of unitary representations of $\\pi_{1}(X)$. We show that this bijective correspondence extends to smooth orbifolds.
Unitary approach to the quantum forced harmonic oscillator
2014-01-01
In this paper we introduce an alternative approach to studying the evolution of a quantum harmonic oscillator subject to an arbitrary time dependent force. With the purpose of finding the evolution operator, certain unitary transformations are applied successively to Schr\\"odinger's equation reducing it to its simplest form. Therefore, instead of solving the original Schr\\"odinger's partial differential equation in time and space the problem is replaced by a system of ordinary differential eq...
Unitary Application of the Quantum Error Correction Codes
Institute of Scientific and Technical Information of China (English)
游波; 许可; 吴小华
2012-01-01
For applying the perfect code to transmit quantum information over a noise channel, the standard protocol contains four steps： the encoding, the noise channel, the error-correction operation, and the decoding. In present work, we show that this protocol can be simplified. The error-correction operation is not necessary if the decoding is realized by the so-called complete unitary transformation. We also offer a quantum circuit, which can correct the arbitrary single-qubit errors.
Unitary-matrix models as exactly solvable string theories
Periwal, Vipul; Shevitz, Danny
1990-01-01
Exact differential equations are presently found for the scaling functions of models of unitary matrices which are solved in a double-scaling limit, using orthogonal polynomials on a circle. For the case of the simplest, k = 1 model, the Painleve II equation with constant 0 is obtained; possible nonperturbative phase transitions exist for these models. Equations are presented for k = 2 and 3, and discussed with a view to asymptotic behavior.
Two Combinations of Unitary Operators and Frame Representations
Institute of Scientific and Technical Information of China (English)
李祚; 朱红鲜; 张慧; 杜鸿科
2005-01-01
In this paper, we prove that the norm closure of all linear combinations of two unitary operators is equal to the norm closure of all invertible operators in B(H). We apply the results to frame representations and give some simple and alternative proofs of the propositions in “P. G. Casazza, Every frame is a sum of three (but not two) orthonormal bases-and other frame representations, J. Fourier Anal. Appl., 4(6)(1998), 727-732.”
Unitary fermions on the lattice I: in a harmonic trap
Endres, Michael G; Lee, Jong-Wan; Nicholson, Amy N
2011-01-01
We present a new lattice Monte Carlo approach developed for studying large numbers of strongly interacting nonrelativistic fermions, and apply it to a dilute gas of unitary fermions confined to a harmonic trap. Our lattice action is highly improved, with sources of discretization and finite volume errors systematically removed; we are able to demonstrate the expected volume scaling of energy levels of two and three untrapped fermions, and to reproduce the high precision calculations published previously for the ground state energies for N = 3 unitary fermions in a box (to within our 0.3% uncertainty), and for N = 3, . . ., 6 unitary fermions in a harmonic trap (to within our ~ 1% uncertainty). We use this action to determine the ground state energies of up to 70 unpolarized fermions trapped in a harmonic potential on a lattice as large as 64^3 x 72; our approach avoids the use of importance sampling or calculation of a fermion determinant and employs a novel statistical method for estimating observables, allo...
Entanglement entropy of non-unitary integrable quantum field theory
Directory of Open Access Journals (Sweden)
Davide Bianchini
2015-07-01
Full Text Available In this paper we study the simplest massive 1+1 dimensional integrable quantum field theory which can be described as a perturbation of a non-unitary minimal conformal field theory: the Lee–Yang model. We are particularly interested in the features of the bi-partite entanglement entropy for this model and on building blocks thereof, namely twist field form factors. Non-unitarity selects out a new type of twist field as the operator whose two-point function (appropriately normalized yields the entanglement entropy. We compute this two-point function both from a form factor expansion and by means of perturbed conformal field theory. We find good agreement with CFT predictions put forward in a recent work involving the present authors. In particular, our results are consistent with a scaling of the entanglement entropy given by ceff3logℓ where ceff is the effective central charge of the theory (a positive number related to the central charge and ℓ is the size of the region. Furthermore the form factor expansion of twist fields allows us to explore the large region limit of the entanglement entropy and find the next-to-leading order correction to saturation. We find that this correction is very different from its counterpart in unitary models. Whereas in the latter case, it had a form depending only on few parameters of the model (the particle spectrum, it appears to be much more model-dependent for non-unitary models.
The Fermiac or Fermi's Trolley
Coccetti, F.
2016-03-01
The Fermiac, known also as Fermi's trolley or Monte Carlo trolley, is an analog computer used to determine the change in time of the neutron population in a nuclear device, via the Monte Carlo method. It was invented by Enrico Fermi and constructed by Percy King at Los Alamos in 1947, and used for about two years. A replica of the Fermiac was built at INFN mechanical workshops of Bologna in 2015, on behalf of the Museo Storico della Fisica e Centro Studi e Ricerche "Enrico Fermi", thanks to the original drawings made available by Los Alamos National Laboratory (LANL). This reproduction of the Fermiac was put in use, and a simulation was developed.
Bhatnagar, Manav R
2012-01-01
In this paper, we derive a maximum likelihood (ML) decoder of the differential data in a decode-and-forward (DF) based cooperative communication system utilizing uncoded transmissions. This decoder is applicable to complex-valued unitary and non-unitary constellations suitable for differential modulation. The ML decoder helps in improving the diversity of the DF based differential cooperative system using an erroneous relaying node. We also derive a piecewise linear (PL) decoder of the differential data transmitted in the DF based cooperative system. The proposed PL decoder significantly reduces the decoding complexity as compared to the proposed ML decoder without any significant degradation in the receiver performance. Existing ML and PL decoders of the differentially modulated uncoded data in the DF based cooperative communication system are only applicable to binary modulated signals like binary phase shift keying (BPSK) and binary frequency shift keying (BFSK), whereas, the proposed decoders are applicab...
The Fermi Paradox is Neither Fermis Nor a Paradox
Gray, Robert H
2016-01-01
The so-called Fermi paradox claims that if technological life existed anywhere else, we would see evidence of its visits to Earth-and since we do not, such life does not exist, or some special explanation is needed. Enrico Fermi, however, never published anything on this topic. On the one occasion he is known to have mentioned it, he asked 'where is everybody?'- apparently suggesting that we don't see extraterrestrials on Earth because interstellar travel may not be feasible, but not suggesting that intelligent extraterrestrial life does not exist, or suggesting its absence is paradoxical. The claim 'they are not here; therefore they do not exist' was first published by Michael Hart, claiming that interstellar travel and colonization of the galaxy would be inevitable if intelligent extraterrestrial life existed, and taking its absence here as proof that it does not exist anywhere. The Fermi paradox appears to originate in Hart's argument, not Fermi's question. Clarifying the origin of these ideas is important...
Structural and quantum properties of van der Waals cluster near the unitary regime
Lekala, M. L.; Chakrabarti, B.; Haldar, S. K.; Roy, R.; Rampho, G. J.
2017-07-01
We study the structural and several quantum properties of three-dimensional bosonic cluster interacting through van der Waals potential at large scattering length. We use Faddeev-type decomposition of the many-body wave function which includes all possible two-body correlations. At large scattering length, we observe spatially extended states which exhibit the exponential dependence on the state number. The cluster ground state energy shows universal nature at large negative scattering length. We also find the existence of generalized Tjon lines for N-body clusters. Signature of universal behaviour of weakly bound clusters can be observed in experiments of ultracold Bose gases. We also study the spectral statistics of the system. We calculate both the short-range fluctuation and long-range correlation and observe semi-Poisson distribution which interpolates the Gaussian Orthogonal Ensemble (GOE) and Poisson statistics of random matrix theory. It indicates that the van der Waal cluster near the unitary becomes highly complex and correlated. However additional study of P (r) distribution (without unfolding of energy spectrum) reveals the possibility of chaos for larger cluster.
... known as: Arterial Blood Gases; ABGs Formal name: Arterial Blood Gas Analysis Related tests: Electrolytes , Bicarbonate , BUN , Creatinine , Emergency and ... lives higher than sea level. Results from an arterial blood gas analysis are not diagnostic; they should be used in ...
Kauzmann, Walter
2012-01-01
Monograph and text supplement for first-year students of physical chemistry focuses chiefly on the molecular basis of important thermodynamic properties of gases, including pressure, temperature, and thermal energy. 1966 edition.
National Research Council Canada - National Science Library
Jacques Arnaud; Laurent Chusseau; Fabrice Philippe
2013-01-01
We show that the thermodynamics of ideal gases may be derived solely from the Democritean concept of corpuscles moving in vacuum plus a principle of simplicity, namely that these laws are independent...
Tabor, David
1969-01-01
It has been tradional to treat gases, liquids and solids as if they were completely unrelated material. However, this book shows that many of their bulk properties can been explained in terms of intermolecular forces.
“Hard probes” of strongly-interacting atomic gases
Energy Technology Data Exchange (ETDEWEB)
Nishida, Yusuke [Los Alamos National Laboratory
2012-06-18
We investigate properties of an energetic atom propagating through strongly interacting atomic gases. The operator product expansion is used to systematically compute a quasiparticle energy and its scattering rate both in a spin-1/2 Fermi gas and in a spinless Bose gas. Reasonable agreement with recent quantum Monte Carlo simulations even at a relatively small momentum k/kF > 1.5 indicates that our large-momentum expansions are valid in a wide range of momentum. We also study a differential scattering rate when a probe atom is shot into atomic gases. Because the number density and current density of the target atomic gas contribute to the forward scattering only, its contact density (measure of short-range pair correlation) gives the leading contribution to the backward scattering. Therefore, such an experiment can be used to measure the contact density and thus provides a new local probe of strongly interacting atomic gases.
Hydrodynamics of Normal Atomic Gases with Spin-orbit Coupling.
Hou, Yan-Hua; Yu, Zhenhua
2015-10-20
Successful realization of spin-orbit coupling in atomic gases by the NIST scheme opens the prospect of studying the effects of spin-orbit coupling on many-body physics in an unprecedentedly controllable way. Here we derive the linearized hydrodynamic equations for the normal atomic gases of the spin-orbit coupling by the NIST scheme with zero detuning. We show that the hydrodynamics of the system crucially depends on the momentum susceptibilities which can be modified by the spin-orbit coupling. We reveal the effects of the spin-orbit coupling on the sound velocities and the dipole mode frequency of the gases by applying our formalism to the ideal Fermi gas. We also discuss the generalization of our results to other situations.
The third virial coefficient of a two-component unitary Fermi gas across an Efimov-effect threshold
Gao, Chao; Endo, Shimpei; Castin, Yvan
2015-01-01
We consider a mixture of two single-spin-state fermions with an interaction of negligible range and infinite s-wave scattering length. By varying the mass ratio α across α_c≃ 13.6069 one can switch on and off the Efimov effect. We determine analytically the third cluster coefficient of the gas. We show that it is a smooth function of α across αc since, unexpectedly, the three-body parameter characterizing the interaction is relevant even on the non-Efimovian side α<αc .
Holography, fermi surfaces and criticality
Čubrović, Mihailo
2013-01-01
We employ the novel method of AdS/CFT correspondence to study strongly correlated fermions, their ground states and the phase transitions between them. AdS/CFT maps the quantum many-body problem to a classical gravity problem, making it more tractable. We find a holographic description of Fermi
Relationship between Fermi Resonance and Solvent Effects
Institute of Scientific and Technical Information of China (English)
JIANG Xiu-Lan; LI Dong-Fei; SUN Cheng-Lin; LI Zhan-Long; YANG Guang; ZHOU Mi; LI Zuo-Wei; GAO Shu-Qin
2011-01-01
We theoretically and experimentally study the relationship between Fermi resonance and solvent effects and investigate the Fermi resonance of p-benzoquinone and cyclopentanone in different solvents and the Fermi resonance of CS2 in C6H6 at different concentrations. Also, we investigate the Fermi resonance of C6H6 and CCl4 in their solution at different pressures. It is found that solvent effects can be utilized to search Fermi resonance parameters such as coupling coefficient and spectral intensity ratio, etc., on the other hand, the mechanism of solvent effects can be revealed according to Fermi resonance at high pressure.%@@ We theoretically and experimentally study the relationship between Fermi resonance and solvent effects and investigate the Fermi resonance of p-benzoquinone and cyclopentanone in different solvents and the Fermi resonance of CS2 in C6H6 at different concentrations.Also,we investigate the Fermi resonance of C6H6 and CCl4 in their solution at different pressures.It is found that solvent effects can be utilized to search Fermi resonance parameters such as coupling coefficient and spectral intensity ratio,etc.,on the other hand,the mechanism of solvent effects can be revealed according to Fermi resonance at high pressure.
STEM education and Fermi problems
Holubova, Renata
2017-01-01
One of the research areas of Physics education is the study of the educational process. Investigations in this area are aimed for example on the teaching and learning process and its results. The conception of STEM education (Science, Technology, Engineering, and Mathematics) is discussed - it is one possible approach to the preparation of the curriculum and the focus on the educational process at basic and secondary schools. At schools in the Czech Republic STEM is much more realized by the application of interdisciplinary relations between subjects Physics-Nature-Technique. In both conceptions the aim is to support pupils' creativity, critical thinking, cross-curricular links. In this context the possibility of using Fermi problems in teaching Physics was discussed (as an interdisciplinary and constructivist activity). The aim of our research was the analysis of Fermi problems solving strategies, the ability of pupils to solve Fermi problems. The outcome of our analysis was to find out methods and teaching strategies which are important to use in teaching - how to solve qualitative and interdisciplinary tasks in physics. In this paper the theoretical basis of STEM education and Fermi problems will be presented. The outcome of our findings based on the research activities will be discussed so as our experiences from 10 years of Fermi problems competition that takes place at the Science Faculty, Palacky University in Olomouc. Changes in competencies of solving tasks by our students (from the point of view in terms of modern, activating teaching methods recommended by theory of Physics education and other science subjects) will be identified.
Cross-talk in phase encoded volume holographic memories employing unitary matrices
Zhang, X.; Berger, G.; Dietz, M.; Denz, C.
2006-12-01
The cross-talk noise in phase encoded holographic memories employing unitary matrices is theoretically investigated. After reviewing some earlier work in this area, we derive a relationship for the noise-to-signal ratio for phase-code multiplexing with unitary matrices. The noise-to-signal ratio rises in a zigzag way on increasing the storage capacity. Cross-talk is mainly caused by high-frequency phase codes. Unitary matrices of even orders have only one bad code, while unitary matrices of odd orders have four bad codes. The signal-to-noise ratios of all other codes can in each case be drastically improved by omission of these bad codes. We summarize the optimal orders of Hadamard and unitary matrices for recording a given number of holograms. The unitary matrices can enable us to adjust the available spatial light modulators to achieve the maximum possible storage capacity in both circumstances with and without bad codes.
Global unitary fixing and matrix-valued correlations in matrix models
Adler, S L; Horwitz, Lawrence P.
2003-01-01
We consider the partition function for a matrix model with a global unitary invariant energy function. We show that the averages over the partition function of global unitary invariant trace polynomials of the matrix variables are the same when calculated with any choice of a global unitary fixing, while averages of such polynomials without a trace define matrix-valued correlation functions, that depend on the choice of unitary fixing. The unitary fixing is formulated within the standard Faddeev-Popov framework, in which the squared Vandermonde determinant emerges as a factor of the complete Faddeev-Popov determinant. We give the ghost representation for the FP determinant, and the corresponding BRST invariance of the unitary-fixed partition function. The formalism is relevant for deriving Ward identities obeyed by matrix-valued correlation functions.
Abstract structure of unitary oracles for quantum algorithms
Directory of Open Access Journals (Sweden)
William Zeng
2014-12-01
Full Text Available We show that a pair of complementary dagger-Frobenius algebras, equipped with a self-conjugate comonoid homomorphism onto one of the algebras, produce a nontrivial unitary morphism on the product of the algebras. This gives an abstract understanding of the structure of an oracle in a quantum computation, and we apply this understanding to develop a new algorithm for the deterministic identification of group homomorphisms into abelian groups. We also discuss an application to the categorical theory of signal-flow networks.
Unitary evolution for a quantum Kantowski-Sachs cosmology
Pal, Sridip
2015-01-01
It is shown that like Bianchi I, V and IX models, a Kantowski-Sachs cosmological model also allows a unitary evolution on quantization. It has also been shown that this unitarity is not at the expense of the anisotropy. Non-unitarity, if there is any, cannot escape notice in this as the evolution is studied against a properly oriented time parameter fixed by the evolution of the fluid. Furthermore, we have constructed a wave-packet by superposing different energy eigenstates, thereby establishing unitarity in a non-trivial way, which is a stronger result than an energy eigenstate trivially giving time independent probability density. For $\\alpha\
Introduction to orthogonal, symplectic and unitary representations of finite groups
Riehm, Carl R
2011-01-01
Orthogonal, symplectic and unitary representations of finite groups lie at the crossroads of two more traditional subjects of mathematics-linear representations of finite groups, and the theory of quadratic, skew symmetric and Hermitian forms-and thus inherit some of the characteristics of both. This book is written as an introduction to the subject and not as an encyclopaedic reference text. The principal goal is an exposition of the known results on the equivalence theory, and related matters such as the Witt and Witt-Grothendieck groups, over the "classical" fields-algebraically closed, rea
Deformations of polyhedra and polygons by the unitary group
Livine, Etera R.
2013-12-01
We introduce the set of framed (convex) polyhedra with N faces as the symplectic quotient {{C}}^{2N}//SU(2). A framed polyhedron is then parametrized by N spinors living in {{C}}2 satisfying suitable closure constraints and defines a usual convex polyhedron plus extra U(1) phases attached to each face. We show that there is a natural action of the unitary group U(N) on this phase space, which changes the shape of faces and allows to map any (framed) polyhedron onto any other with the same total (boundary) area. This identifies the space of framed polyhedra to the Grassmannian space U(N)/ (SU(2)×U(N-2)). We show how to write averages of geometrical observables (polynomials in the faces' area and the angles between them) over the ensemble of polyhedra (distributed uniformly with respect to the Haar measure on U(N)) as polynomial integrals over the unitary group and we provide a few methods to compute these integrals systematically. We also use the Itzykson-Zuber formula from matrix models as the generating function for these averages and correlations. In the quantum case, a canonical quantization of the framed polyhedron phase space leads to the Hilbert space of SU(2) intertwiners (or, in other words, SU(2)-invariant states in tensor products of irreducible representations). The total boundary area as well as the individual face areas are quantized as half-integers (spins), and the Hilbert spaces for fixed total area form irreducible representations of U(N). We define semi-classical coherent intertwiner states peaked on classical framed polyhedra and transforming consistently under U(N) transformations. And we show how the U(N) character formula for unitary transformations is to be considered as an extension of the Itzykson-Zuber to the quantum level and generates the traces of all polynomial observables over the Hilbert space of intertwiners. We finally apply the same formalism to two dimensions and show that classical (convex) polygons can be described in a
UV radiation sensors with unitary and binary superficial barrier
Dorogan, Valerian; Vieru, Tatiana; Kosyak, V.; Damaskin, I.; Chirita, F.
1998-07-01
UV radiation sensors with unitary and binary superficial barrier, made on the basis of GaP - SnO2 and GaAs - AlGaAs - SnO2 heterostructures, are presented in the paper. Technological and constructive factors, which permit to realize a high conversion efficiency and to exclude the influence of visible spectrum upon the photoanswer, are analyzed. It was established that the presence of an isotypical superficial potential barrier permits to suppress the photoanswer component formed by absorption of visible and infrared radiation in semiconductor structure bulk.
Non-unitary neutrino propagation from neutrino decay
Directory of Open Access Journals (Sweden)
Jeffrey M. Berryman
2015-03-01
Full Text Available Neutrino propagation in space–time is not constrained to be unitary if very light states – lighter than the active neutrinos – exist into which neutrinos may decay. If this is the case, neutrino flavor-change is governed by a handful of extra mixing and “oscillation” parameters, including new sources of CP-invariance violation. We compute the transition probabilities in the two- and three-flavor scenarios and discuss the different phenomenological consequences of the new physics. These are qualitatively different from other sources of unitarity violation discussed in the literature.
Multiscale differential phase contrast analysis with a unitary detector
Lopatin, Sergei
2015-12-30
A new approach to generate differential phase contrast (DPC) images for the visualization and quantification of local magnetic fields in a wide range of modern nano materials is reported. In contrast to conventional DPC methods our technique utilizes the idea of a unitary detector under bright field conditions, making it immediately usable by a majority of modern transmission electron microscopes. The approach is put on test to characterize the local magnetization of cylindrical nanowires and their 3D ordered arrays, revealing high sensitivity of our method in a combination with nanometer-scale spatial resolution.
Non-unitary neutrino propagation from neutrino decay
Energy Technology Data Exchange (ETDEWEB)
Berryman, Jeffrey M., E-mail: jeffreyberryman2012@u.northwestern.edu [Northwestern University, Department of Physics & Astronomy, 2145 Sheridan Road, Evanston, IL 60208 (United States); Gouvêa, André de; Hernández, Daniel [Northwestern University, Department of Physics & Astronomy, 2145 Sheridan Road, Evanston, IL 60208 (United States); Oliveira, Roberto L.N. [Northwestern University, Department of Physics & Astronomy, 2145 Sheridan Road, Evanston, IL 60208 (United States); Instituto de Física Gleb Wataghin Universidade Estadual de Campinas, UNICAMP 13083-970, Campinas, São Paulo (Brazil)
2015-03-06
Neutrino propagation in space-time is not constrained to be unitary if very light states – lighter than the active neutrinos – exist into which neutrinos may decay. If this is the case, neutrino flavor-change is governed by a handful of extra mixing and “oscillation” parameters, including new sources of CP-invariance violation. We compute the transition probabilities in the two- and three-flavor scenarios and discuss the different phenomenological consequences of the new physics. These are qualitatively different from other sources of unitarity violation discussed in the literature.
Computing a logarithm of a unitary matrix with general spectrum
Loring, Terry A
2012-01-01
In theory, a unitary matrix U has a skew-hermitian logarithm H. In a computing environment one expects only to know U^*U \\approx I and might wish to compute H with e^H \\approx U and H^*= -H. This is relatively easy to accomplish using the Schur decomposition. Reasonable error bounds are derived. In cases where the norm of U^*U-I is somewhat large we discuss the utility of pre-processing with Newton's method of approximating the polar decomposition. In the case of U being J-skew-symmetric, one can insist that H be J-skew-symmetric and skew-Hermitian.
Thermoelectric-induced unitary Cooper pair splitting efficiency
Energy Technology Data Exchange (ETDEWEB)
Cao, Zhan; Fang, Tie-Feng [Center for Interdisciplinary Studies and Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Li, Lin [Department of Physics, Southern University of Science and Technology of China, Shenzhen 518005 (China); Luo, Hong-Gang [Center for Interdisciplinary Studies and Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Beijing Computational Science Research Center, Beijing 100084 (China)
2015-11-23
Thermoelectric effect is exploited to optimize the Cooper pair splitting efficiency in a Y-shaped junction, which consists of two normal leads coupled to an s-wave superconductor via double noninteracting quantum dots. Here, utilizing temperature difference rather than bias voltage between the two normal leads, and tuning the two dot levels such that the transmittance of elastic cotunneling process is particle-hole symmetric, we find current flowing through the normal leads are totally contributed from the splitting of Cooper pairs emitted from the superconductor. Such a unitary splitting efficiency is significantly better than the efficiencies obtained in experiments so far.
Implementing controlled-unitary operations over the butterfly network
Soeda, Akihito; Kinjo, Yoshiyuki; Turner, Peter S.; Murao, Mio
2014-12-01
We introduce a multiparty quantum computation task over a network in a situation where the capacities of both the quantum and classical communication channels of the network are limited and a bottleneck occurs. Using a resource setting introduced by Hayashi [1], we present an efficient protocol for performing controlled-unitary operations between two input nodes and two output nodes over the butterfly network, one of the most fundamental networks exhibiting the bottleneck problem. This result opens the possibility of developing a theory of quantum network coding for multiparty quantum computation, whereas the conventional network coding only treats multiparty quantum communication.
Unitary cycles on Shimura curves and the Shimura lift II
Sankaran, Siddarth
2013-01-01
We consider two families of arithmetic divisors defined on integral models of Shimura curves. The first was studied by Kudla, Rapoport and Yang, who proved that if one assembles these divisors in a formal generating series, one obtains the q-expansion of a modular form of weight 3/2. The present work concerns the Shimura lift of this modular form: we identify the Shimura lift with a generating series comprised of unitary divisors, which arose in recent work of Kudla and Rapoport regarding cyc...
Luria: a unitary view of human brain and mind.
Mecacci, Luciano
2005-12-01
Special questions the eminent Russian psychologist and neuropsychologist Aleksandr R. Luria (1902-1977) dealt with in his research regarded the relationship between animal and human brain, child and adult mind, normal and pathological, theory and rehabilitation, clinical and experimental investigation. These issues were integrated in a unitary theory of cerebral and psychological processes, under the influence of both different perspectives active in the first half of the Nineteenth century (psychoanalysis and historical-cultural school, first of all) and the growing contribution of neuropsychological research on brain-injured patients.
Implementing controlled-unitary operations over the butterfly network
Energy Technology Data Exchange (ETDEWEB)
Soeda, Akihito; Kinjo, Yoshiyuki; Turner, Peter S. [Department of Physics, Graduate School of Science, The University of Tokyo, Tokyo (Japan); Murao, Mio [Department of Physics, Graduate School of Science, The University of Tokyo, Tokyo, Japan and NanoQuine, The University of Tokyo, Tokyo (Japan)
2014-12-04
We introduce a multiparty quantum computation task over a network in a situation where the capacities of both the quantum and classical communication channels of the network are limited and a bottleneck occurs. Using a resource setting introduced by Hayashi [1], we present an efficient protocol for performing controlled-unitary operations between two input nodes and two output nodes over the butterfly network, one of the most fundamental networks exhibiting the bottleneck problem. This result opens the possibility of developing a theory of quantum network coding for multiparty quantum computation, whereas the conventional network coding only treats multiparty quantum communication.
Graphical description of unitary transformations on hypergraph states
Gachechiladze, Mariami; Tsimakuridze, Nikoloz; Gühne, Otfried
2017-05-01
Hypergraph states form a family of multiparticle quantum states that generalizes cluster states and graph states. We study the action and graphical representation of nonlocal unitary transformations between hypergraph states. This leads to a generalization of local complementation and graphical rules for various gates, such as the CNOT gate and the Toffoli gate. As an application, we show that already for five qubits local Pauli operations are not sufficient to check local equivalence of hypergraph states. Furthermore, we use our rules to construct entanglement witnesses for three-uniform hypergraph states.
Simulating Entangling Unitary Operator Using Non-maximally Entangled States
Institute of Scientific and Technical Information of China (English)
LI Chun-Xian; WANG Cheng-Zhi; NIE Liu-Ying; LI Jiang-Fan
2009-01-01
We use non-maximally entangled states (NMESs) to simulate an entangling unitary operator (EUO) w/th a certain probability. Given entanglement resources, the probability of the success we achieve is a decreasing function of the parameters of the EUO. Given an EUO, for certain entanglement resources the result is optimal, i.e., the probability obtains a maximal value, and for optimal result higher parameters of the EUO match more amount of entanglement resources. The probability of the success we achieve is higher than the known results under some condition.
The science of unitary human beings and interpretive human science.
Reeder, F
1993-01-01
Natural science and human science are identified as the bases of most nursing theories and research programs. Natural science has been disclaimed by Martha Rogers as the philosophy of science that undergirds her work. The question remains, is the science of unitary human beings an interpretive human science? The author explores the works of Rogers through a dialectic with two human scientists' works. Wilhelm Dilthey's works represent the founding or traditional view, and Jurgen Habermas' works represent a contemporary, reconstructionist view. The ways Rogerian thought contributes to human studies but is distinct from traditional and reconstructionist human sciences are illuminated.
Feneric Fermi Size Enhancement of Pairing in Mesoscopic Fermi Systems
Farine, M; Schuck, P; Viñas, X
2002-01-01
The finite size dependent enhancement of pairing in mesoscopic Fermi systems is studied under the assumption that the BCS approach is valid and that the two body force is size independent. Different systems are investigated such as superconducting metallic grains and films as well as atomic nuclei. It is shown that the finite size enhancement of pairing in these systems is a surface effect which, when properly included, accounts for the data.
Dimensionality and Finite Number Effect on BCS Transition of Atomic Fermi Gas
Institute of Scientific and Technical Information of China (English)
CUI Hai-Tao; WANG Lin-Cheng; YI Xue-Xi
2005-01-01
The effect of finite number and dimensionality has been discussed in this paper. The finite number effect has a negative correction to final temperature for 2D or 3D atomic Fermi gases. The changing of final temperature obtained by scanning from BEC region to BCS region are 10% or so with N ≤ 103 and can be negligible when N ＞ 103.However, in 1D atomic Fermi gas, the effect gives a positive correction which greatly changes the final temperature in Fermi gas. This behavior is completely opposed to the 2D and 3D cases and a proper explanation is still to be found.Dimensionality also has a positive correction, in which the more tightly trapping, the higher final temperature one gets with the same particle number. A discussion is also presented.
Kitaev honeycomb tensor networks: exact unitary circuits and applications
Schmoll, Philipp
2016-01-01
The Kitaev honeycomb model is a paradigm of exactly-solvable models, showing non-trivial physical properties such as topological quantum order, abelian and non-abelian anyons, and chirality. Its solution is one of the most beautiful examples of the interplay of different mathematical techniques in condensed matter physics. In this paper, we show how to derive a tensor network (TN) description of the eigenstates of this spin-1/2 model in the thermodynamic limit, and in particular for its ground state. In our setting, eigenstates are naturally encoded by an exact 3d TN structure made of fermionic unitary operators, corresponding to the unitary quantum circuit building up the many-body quantum state. In our derivation we review how the different "solution ingredients" of the Kitaev honeycomb model can be accounted for in the TN language, namely: Jordan-Wigner transformation, braidings of Majorana modes, fermionic Fourier transformation, and Bogoliubov transformation. The TN built in this way allows for a clear u...
On the construction of unitary quantum group differential calculus
Pyatov, Pavel
2016-10-01
We develop a construction of the unitary type anti-involution for the quantized differential calculus over {{GL}}q(n) in the case | q| =1. To this end, we consider a joint associative algebra of quantized functions, differential forms and Lie derivatives over {{GL}}q(n)/{{SL}}q(n), which is bicovariant with respect to {{GL}}q(n)/{{SL}}q(n) coactions. We define a specific non-central spectral extension of this algebra by the spectral variables of three matrices of the algebra generators. In the spectrally expended algebra, we construct a three-parametric family of its inner automorphisms. These automorphisms are used for the construction of the unitary anti-involution for the (spectrally extended) calculus over {{GL}}q(n). This work has been funded by the Russian Academic Excellence Project ‘5-100’. The results of section 5 (propositions 5.2, 5.3 and theorem 5.5) have been obtained under support of the RSF grant No.16-11-10160.
Event-specific versus unitary causal accounts of optimism bias.
Chua, F J; Job, R F
1999-10-01
Optimism bias is often assumed to have a unitary cause regardless of the event, however, factors causing it may actually be event-specific. In Experiment 1 (N = 23), subjects rated the importance of various causes for individual events. The results identified consistent differences in perceptions of causal factors across events. Experiment 2 (N = 190) employed the possible causal factors absent/exempt error and degree of motivation to investigate an event-specific theory of optimism bias in a manipulation design. Participants were encouraged to view one causal factor (absent/exempt or motivation) as either important or unimportant to future risk when they estimated their risk of absent/exempt-related, motivation-related and unrelated events (as determined in Experiment 1). A hanging control group received no manipulation. The event-specific theory's prediction that these manipulations would affect particular events and not others were not supported. However, discouraging the absent/exempt error reduced optimism bias across events, generally. Hence, a unitary and not an event-specific theory of optimism bias was supported. Furthermore, for the first time, the possible role of and confounding of cognitive manipulations of optimism bias by mood were evaluated, and not supported.
Universal Structure and Universal PDE for Unitary Ensembles
Rumanov, Igor
2009-01-01
An attempt is made to describe random matrix ensembles with unitary invariance of measure (UE) in a unified way, using a combination of Tracy-Widom (TW) and Adler-Shiota-Van Moerbeke (ASvM) approaches to derivation of partial differential equations (PDE) for spectral gap probabilities. First, general 3-term recurrence relations for UE restricted to subsets of real line, or, in other words, for functions in the resolvent kernel, are obtained. Using them, simple universal relations between all TW dependent variables and one-dimensional Toda lattice $\\tau$-functions are found. A universal system of PDE for UE is derived from previous relations, which leads also to a {\\it single independent PDE} for spectral gap probability of various UE. Thus, orthogonal function bases and Toda lattice are seen at the core of correspondence of different approaches. Moreover, Toda-AKNS system provides a common structure of PDE for unitary ensembles. Interestingly, this structure can be seen in two very different forms: one arises...
Boson-Faddeev in the Unitary Limit and Efimov States
K"\\ohler, H S
2010-01-01
A numerical study of the Faddeev equation for bosons is made with two-body interactions at or close to the Unitary limit. Separable interactions are obtained from phase-shifts defined by scattering length and effective range. In EFT-language this would correspond to NLO. Both ground and Efimov state energies are calculated. For effective ranges $r_0 > 0$ and rank-1 potentials the total energy $E_T$ is found to converge with momentum cut-off $\\Lambda$ for $\\Lambda > \\sim 10/r_0$ . In the Unitary limit ($1/a=r_0= 0$) the energy does however diverge. It is shown (analytically) that in this case $E_T=E_u\\Lambda^2$. Calculations give $E_u=-0.108$ for the ground state and $E_u=-1.\\times10^{-4}$ for the single Efimov state found. The cut-off divergence is remedied by modifying the off-shell t-matrix by replacing the rank-1 by a rank-2 phase-shift equivalent potential. This is somewhat similar to the counterterm method suggested by Bedaque et al. This investigation is exploratory and does not refer to any specific ph...
Cai, Rong-Gen; Qi, Yong-Hui; Wu, Yue-Liang; Zhang, Yun-Long
2017-06-01
The (2 +1 )-dimensional non-Fermi liquid (NFL) has a dual description in the (3 +1 )-dimensional anti-de Sitter (AdS) spacetime. We begin with a dyonic Reissner-Nordstrom (RN) black brane background, and consider the bulk Dirac fermion field coupled with the background U (1 ) gauge field, as well an intrinsic axial gauge field which is induced by chiral anomaly. The axial gauge field is effectively induced from the topological term in the bulk, which would lead to nontrivial effects on the boundary NFL. We study these effects through calculating the retarded Green's functions of the dual NFL holographically, in both analytical and numerical approaches. We also obtain correlation functions in the low frequency limit at zero and finite temperatures, as well as the dispersion spectrum of the Dirac cones, Fermi arc of the surface states, which can be related with the experiment.
Fermi resonance in optical microcavities
Yi, Chang-Hwan; Yu, Hyeon-Hye; Lee, Ji-Won; Kim, Chil-Min
2015-04-01
Fermi resonance is a phenomenon of quantum mechanical superposition, which most often occurs between normal and overtone modes in molecular systems that are nearly coincident in energy. We find that scarred resonances in deformed dielectric microcavities are the very phenomenon of Fermi resonance, that is, a pair of quasinormal modes interact with each other due to coupling and a pair of resonances are generated through an avoided resonance crossing. Then the quantum number difference of a pair of quasinormal modes, which is a consequence of quantum mechanical superposition, equals periodic orbits, whereby the resonances are localized on the periodic orbits. We derive the relation between the quantum number difference and the periodic orbits and confirm it in an elliptic, a rectangular, and a stadium-shaped dielectric microcavity.
DEFF Research Database (Denmark)
Jensen, Arne; Nenciu, Gheorghe
2008-01-01
We review and further develop the framework in [9] of the stationary theory of resonances, arising by perturbation of either threshold, or embedded in the continuum, eigenvalues. While in [9] only non/degenerate eigenvalues were considered, here we add some results for the degenerate case. [9] A........ Jensen and G. Nenciu, The Fermi Golden Rule and its form at thresholds in odd dimensions. Comm. Math. Phys 261 (2006), 693-727...
Cai, Rong-Gen; Wu, Yue-Liang; Zhang, Yun-Long
2016-01-01
In this paper we investigate the $(2+1)$-dimensional topological non-Fermi liquid in strongly correlated electron system, which has a holographic dual description by Einstein gravity in $(3+1)$-dimensional anti-de Sitter (AdS) space-time. In a dyonic Reissner-Nordstrom black hole background, we consider a Dirac fermion coupled to the background $U(1)$ gauge theory and an intrinsic chiral gauge field $b_M$ induced by chiral anomaly. UV retarded Green's function of the charged fermion in the UV boundary from AdS$_4$ gravity is calculated, by imposing in-falling wave condition at the horizon. We also obtain IR correlation function of the charged fermion at the IR boundary arising from the near horizon geometry of the topological black hole with index $k=0,\\pm 1$. By using the UV retarded Green's function and IR correlation function, we analyze the low frequency behavior of the topological non-Fermi liquid at zero and finite temperatures, especially the relevant non-Fermi liquid behavior near the quantum critical...
Enrico Fermi and the Dolomites
Battimelli, Giovanni
2014-01-01
Summer vacations in the Dolomites were a tradition among the professors of the Faculty of Mathematical and Physical Sciences at the University of Roma since the end of the XIX century. Beyond the academic walls, people like Tullio Levi-Civita, Federigo Enriques and Ugo Amaldi sr., together with their families, were meeting friends and colleagues in Cortina, San Vito, Dobbiaco, Vigo di Fassa and Selva, enjoying trekking together with scientific discussions. The tradition was transmitted to the next generations, in particular in the first half of the XX century, and the group of via Panisperna was directly connected: Edoardo Amaldi, the son of the mathematician Ugo sr., rented at least during two summers, in 1925 and in 1949, and in the winter of 1960, a house in San Vito di Cadore, and almost every year in the Dolomites; Enrico Fermi was a frequent guest. Many important steps in modern physics, in particular the development of the Fermi-Dirac statistics and the Fermi theory of beta decay, are related to scient...
Fermi Timing and Synchronization System
Energy Technology Data Exchange (ETDEWEB)
Wilcox, R.; Staples, J.; Doolittle, L.; Byrd, J.; Ratti, A.; Kaertner, F.X.; Kim, J.; Chen, J.; Ilday, F.O.; Ludwig, F.; Winter, A.; Ferianis, M.; Danailov, M.; D' Auria, G.
2006-07-19
The Fermi FEL will depend critically on precise timing of its RF, laser and diagnostic subsystems. The timing subsystem to coordinate these functions will need to reliably maintain sub-100fs synchronicity between distant points up to 300m apart in the Fermi facility. The technology to do this is not commercially available, and has not been experimentally demonstrated in a working facility. Therefore, new technology must be developed to meet these needs. Two approaches have been researched by different groups working with the Fermi staff. At MIT, a pulse transmission scheme has been developed for synchronization of RF and laser devices. And at LBL, a CW transmission scheme has been developed for RF and laser synchronization. These respective schemes have advantages and disadvantages that will become better understood in coming years. This document presents the work done by both teams, and suggests a possible system design which integrates them both. The integrated system design provides an example of how choices can be made between the different approaches without significantly changing the basic infrastructure of the system. Overall system issues common to any synchronization scheme are also discussed.
Enrico Fermi and the Dolomites
Energy Technology Data Exchange (ETDEWEB)
Battimelli, Giovanni, E-mail: giovanni.battimelli@uniroma1.it; Angelis, Alessandro de, E-mail: alessandro.de.angelis@cern.ch
2014-11-15
Summer vacations in the Dolomites were a tradition among the professors of the Faculty of Mathematical and Physical Sciences at the University of Roma since the end of the XIX century. Beyond the academic walls, people like Tullio Levi-Civita, Federigo Enriques and Ugo Amaldi sr., together with their families, were meeting friends and colleagues in Cortina, San Vito, Dobbiaco, Vigo di Fassa and Selva, enjoying trekking together with scientific discussions. The tradition was transmitted to the next generations, in particular in the first half of the XX century, and the group of via Panisperna was directly connected: Edoardo Amaldi, the son of the mathematician Ugo sr., rented at least during two summers, in 1925 and in 1949, and in the winter of 1960, a house in San Vito di Cadore, and almost every year in the Dolomites; Enrico Fermi was a frequent guest. Many important steps in modern physics, in particular the development of the Fermi-Dirac statistics and the Fermi theory of beta decay, are related to scientific discussions held in the region of the Dolomites.
Enrico Fermi and the Dolomites
Battimelli, Giovanni; de Angelis, Alessandro
2014-11-01
Summer vacations in the Dolomites were a tradition among the professors of the Faculty of Mathematical and Physical Sciences at the University of Roma since the end of the XIX century. Beyond the academic walls, people like Tullio Levi-Civita, Federigo Enriques and Ugo Amaldi sr., together with their families, were meeting friends and colleagues in Cortina, San Vito, Dobbiaco, Vigo di Fassa and Selva, enjoying trekking together with scientific discussions. The tradition was transmitted to the next generations, in particular in the first half of the XX century, and the group of via Panisperna was directly connected: Edoardo Amaldi, the son of the mathematician Ugo sr., rented at least during two summers, in 1925 and in 1949, and in the winter of 1960, a house in San Vito di Cadore, and almost every year in the Dolomites; Enrico Fermi was a frequent guest. Many important steps in modern physics, in particular the development of the Fermi-Dirac statistics and the Fermi theory of beta decay, are related to scientific discussions held in the region of the Dolomites.
Efimov correlations in strongly interacting Bose gases
Hofmann, Johannes; Barth, Marcus
A series of recent hallmark experiments have demonstrated that Bose gases can be created in the strongly interacting unitary limit in the non-degenerate high-temperature regime. These systems display the three-body Efimov effect, which poses a theoretical challenge to compute observables including these relevant three-body correlations. In this talk, I shall present our results for the virial coefficients, the contact parameters, and the momentum distribution of a strongly interacting three-dimensional Bose gas obtained by means of a virial expansion up to third order in the fugacity, which takes into account three-body correlations exactly. Our results characterize the non-degenerate regime of the interacting Bose gas, where the thermal wavelength is smaller than the interparticle spacing but the scattering length may be arbitrarily large. In addition, we provide a calculation of the momentum distribution at unitarity, which displays a universal high-momentum tail with a log-periodic momentum dependence - a direct signature of Efimov physics. In particular, we provide a quantitative description of the momentum distribution at high momentum as measured by the JILA group [Makotyn et al., Nat. Phys. 10, 116 (2014)]. Our results allow the spectroscopy of Efimov states at unitarity.
Fermi/non-Fermi mixing in SU($N$) Kondo effect
Kimura, Taro
2016-01-01
We apply conformal field theory analysis to the $k$-channel SU($N$) Kondo system, and find a peculiar behavior in the cases $N > k > 1$, which we call Fermi/non-Fermi mixing: The low temperature scaling is described as the Fermi liquid, while the zero temperature IR fixed point exhibits the non-Fermi liquid signature. We also show that the Wilson ratio is no longer universal for the cases $N > k > 1$. The deviation from the universal value of the Wilson ratio could be used as an experimental signal of the Fermi/non-Fermi mixing.
All-optical production of 6Li quantum gases
Burchianti, A.; Seman, J. A.; Valtolina, G.; Morales, A.; Inguscio, M.; Zaccanti, M.; Roati, G.
2015-03-01
We report efficient production of quantum gases of 6Li using a sub-Doppler cooling scheme based on the D1 transition. After loading in a standard magneto-optical trap, an atomic sample of 109 atoms is cooled at a temperature of 40 μK by a bichromatic D1 gray-molasses. More than 2×107 atoms are then transferred into a high-intensity optical dipole trap, where a two-spin state mixture is evaporatively cooled down to quantum degeneracy. We observe that D1 cooling remains effective in the deep trapping potential, allowing an effective increase of the atomic phase-space density before starting the evaporation. In a total experimental cycle of 11 s, we produce weakly-interacting degenerate Fermi gases of 7×105 atoms at T/TF molecules. We further describe a simple and compact optical system both for high-resolution imaging and for imprinting a thin optical barrier on the atomic cloud; this represents a first step towards the study of quantum tunneling in strongly interacting superfluid Fermi gases.
Energy Technology Data Exchange (ETDEWEB)
Mazaud, J.P.
1996-06-01
The natural gas or naphtha are the main constituents used for the production of synthetic gases. Several production ways of synthetic gases are industrially used as for example the natural gas or naphtha catalytic reforming, the selective oxidation of natural gas or heavy fuels and the coal oxy-vapo-gasification. The aim of this work is to study the different steps of production and treatment of the synthetic gases by the way of catalytic reforming. The first step is the desulfurization of the hydrocarbons feedstocks. The process used in industry is described. Then is realized the catalytic hydrocarbons reforming process. After having recalled some historical data on the catalytic reforming, the author gives the reaction kinetics and thermodynamics. The possible reforming catalysts, industrial equipments and furnaces designs are then exposed. The carbon dioxide is a compound easily obtained during the reforming reactions. It is a wasteful and harmful component which has to be extracted of the gaseous stream. The last step is then the gases de-carbonation. Two examples of natural gas or naphtha reforming reactions are at last given: the carbon monoxide conversion by steam and the carbon oxides reactions with hydrogen (methanization). (O.M.). 8 figs., 6 tabs.
Compactifications of the Heterotic string with unitary bundles
Energy Technology Data Exchange (ETDEWEB)
Weigand, T.
2006-05-23
In this thesis we investigate a large new class of four-dimensional supersymmetric string vacua defined as compactifications of the E{sub 8} x E{sub 8} and the SO(32) heterotic string on smooth Calabi-Yau threefolds with unitary gauge bundles and heterotic five-branes. The first part of the thesis discusses the implementation of this idea into the E{sub 8} x E{sub 8} heterotic string. After specifying a large class of group theoretic embeddings featuring unitary bundles, we analyse the effective four-dimensional N=1 supergravity upon compactification. From the gauge invariant Kaehler potential for the moduli fields we derive a modification of the Fayet-Iliopoulos D-terms arising at one-loop in string perturbation theory. From this we conjecture a one-loop deformation of the Hermitian Yang-Mills equation and introduce the idea of {lambda}-stability as the perturbatively correct stability concept generalising the notion of Mumford stability valid at tree-level. We then proceed to a definition of SO(32) heterotic vacua with unitary gauge bundles in the presence of heterotic five-branes and find agreement of the resulting spectrum with the S-dual framework of Type I/Type IIB orientifolds. A similar analysis of the effective four-dimensional supergravity is performed. Further evidence for the proposed one-loop correction to the stability condition is found by identifying the heterotic corrections as the S-dual of the perturbative part of {pi}-stability as the correct stability concept in Type IIB theory. After reviewing the construction of holomorphic stable vector bundles on elliptically fibered Calabi-Yau manifolds via spectral covers, we provide semi-realistic examples for SO(32) heterotic vacua with Pati-Salam and MSSM-like gauge sectors. We finally discuss the construction of realistic vacua with flipped SU(5) GUT and MSSM gauge group within the E{sub 8} x E{sub 8} framework, based on the embedding of line bundles into both E{sub 8} factors. Some of the appealing
The Schur algorithm for generalized Schur functions III : J-unitary matrix polynomials on the circle
Alpay, Daniel; Azizov, Tomas; Dijksma, Aad; Langer, Heinz
2003-01-01
The main result is that for J = ((1)(0) (0)(-1)) every J-unitary 2 x 2-matrix polynomial on the unit circle is an essentially unique product of elementary J-unitary 2 x 2-matrix polynomials which are either of degree 1 or 2k. This is shown by means of the generalized Schur transformation introduced
47 CFR 65.101 - Initiation of unitary rate of return prescription proceedings.
2010-10-01
... 47 Telecommunication 3 2010-10-01 2010-10-01 false Initiation of unitary rate of return...) COMMON CARRIER SERVICES (CONTINUED) INTERSTATE RATE OF RETURN PRESCRIPTION PROCEDURES AND METHODOLOGIES Procedures § 65.101 Initiation of unitary rate of return prescription proceedings. (a) Whenever...
Wanjala, G; Kaashoek, MA; Seatzu, S; VanDerMee, C
2005-01-01
A generalized Schur function which is holomorphic at z = 0 can be written as the characteristic function of a closely connected unitary colligation with a Pontryagin state space. We describe the closely connected unitary colligation of a solution s(z) of the basic interpolation problem for generaliz
Molecular Quantum Computing by an Optimal Control Algorithm for Unitary Transformations
Palao, J P; Palao, Jose P.; Kosloff, Ronnie
2002-01-01
Quantum computation is based on implementing selected unitary transformations which represent algorithms. A generalized optimal control theory is used to find the driving field that generates a prespecified unitary transformation. The approach is illustrated in the implementation of one and two qubits gates in model molecular systems.
Landau Theory of Helical Fermi Liquids.
Lundgren, Rex; Maciejko, Joseph
2015-08-07
We construct a phenomenological Landau theory for the two-dimensional helical Fermi liquid found on the surface of a three-dimensional time-reversal invariant topological insulator. In the presence of rotation symmetry, interactions between quasiparticles are described by ten independent Landau parameters per angular momentum channel, by contrast with the two (symmetric and antisymmetric) Landau parameters for a conventional spin-degenerate Fermi liquid. We project quasiparticle states onto the Fermi surface and obtain an effectively spinless, projected Landau theory with a single projected Landau parameter per angular momentum channel that captures the spin-momentum locking or nontrivial Berry phase of the Fermi surface. As a result of this nontrivial Berry phase, projection to the Fermi surface can increase or lower the angular momentum of the quasiparticle interactions. We derive equilibrium properties, criteria for Fermi surface instabilities, and collective mode dispersions in terms of the projected Landau parameters. We briefly discuss experimental means of measuring projected Landau parameters.
Unitary equilibrations: probability distribution of the Loschmidt echo
Venuti, Lorenzo Campos
2009-01-01
Closed quantum systems evolve unitarily and therefore cannot converge in a strong sense to an equilibrium state starting out from a generic pure state. Nevertheless for large system size one observes temporal typicality. Namely, for the overwhelming majority of the time instants, the statistics of observables is practically indistinguishable from an effective equilibrium one. In this paper we consider the Loschmidt echo (LE) to study this sort of unitary equilibration after a quench. We draw several conclusions on general grounds and on the basis of an exactly-solvable example of a quasi-free system. In particular we focus on the whole probability distribution of observing a given value of the LE after waiting a long time. Depending on the interplay between the initial state and the quench Hamiltonian, we find different regimes reflecting different equilibration dynamics. When the perturbation is small and the system is away from criticality the probability distribution is Gaussian. However close to criticali...
Husserlian phenomenology and nursing in a unitary-transformative paradigm
DEFF Research Database (Denmark)
Hall, Elisabeth
1996-01-01
The aim of this article is to discuss Husserlian phenomenology as philosophy and methodology, and its relevance for nursing research. The main content in Husserl's phenomenological world view is described and compared to the unitary-transformative paradigm as mentioned by Newman et al....... The phenomenological methodology according to Spiegelberg is described, and exemplified through the author's ongoing study. Different critiques of phenomenology and phenomenological reports are mentioned, and the phenomenological description is illustrated as the metaphor «using a handful of colors». The metaphor...... is used to give phenomenological researchers and readers an expanding reality picturing, including memories and hopes and not only a reality of the five senses. It is concluded that phenomenology as a world view and methodology can contribute to nursing research and strengthen the identity of nursing...
Momentum Distribution in the Unitary Bose Gas from First Principles
Comparin, Tommaso; Krauth, Werner
2016-11-01
We consider a realistic bosonic N -particle model with unitary interactions relevant for Efimov physics. Using quantum Monte Carlo methods, we find that the critical temperature for Bose-Einstein condensation is decreased with respect to the ideal Bose gas. We also determine the full momentum distribution of the gas, including its universal asymptotic behavior, and compare this crucial observable to recent experimental data. Similar to the experiments with different atomic species, differentiated solely by a three-body length scale, our model only depends on a single parameter. We establish a weak influence of this parameter on physical observables. In current experiments, the thermodynamic instability of our model from the atomic gas towards an Efimov liquid could be masked by the dynamical instability due to three-body losses.
The Reid93 Potential Triton in the Unitary Pole Approximation
Afnan, I. R.; Gibson, B. F.
2013-12-01
The Reid93 potential provides a representation of the nucleon-nucleon ( NN) scattering data that rivals that of a partial wave analysis. We present here a unitary pole approximation (UPA) for this contemporary NN potential that provides a rank one separable potential for which the wave function of the deuteron (3S1-3D1) and singlet anti-bound (1S0) state are exactly those of the original potential. Our motivation is to use this UPA potential to investigate the sensitivity of the electric dipole moment for the deuteron and 3H and 3He to the ground state nuclear wave function. We compare the Reid93 results with those for the original Reid (Reid68) potential to illustrate the accuracy of the bound state properties.
Unitary theory of pion photoproduction in the chiral bag model
Energy Technology Data Exchange (ETDEWEB)
Araki, M.; Afnan, I.R.
1987-07-01
We present a multichannel unitary theory of single pion photoproduction from a baryon B. Here, B is the nucleon or ..delta..(1232), with possible extension to include the Roper resonance and strange baryons. We treat the baryon as a three-quark state within the framework of the gauge and chiral Lagrangian, derived from the Lagrangian for the chiral bag model. By first exposing two-body, and then three-body unitarity, taking into consideration the ..pi pi..B and ..gamma pi..B intermediate states, we derive a set of equations for the amplitudes both on and off the energy shell. The Born term in the expansion of the amplitude has the new feature that the vertices in the pole diagram are undressed, while those in the crossed, contact, and pion pole diagrams are dressed.
Unitary theory of pion photoproduction in the chiral bag model
Araki, M.; Afnan, I. R.
1987-07-01
We present a multichannel unitary theory of single pion photoproduction from a baryon B. Here, B is the nucleon or Δ(1232), with possible extension to include the Roper resonance and strange baryons. We treat the baryon as a three-quark state within the framework of the gauge and chiral Lagrangian, derived from the Lagrangian for the chiral bag model. By first exposing two-body, and then three-body unitarity, taking into consideration the ππB and γπB intermediate states, we derive a set of equations for the amplitudes both on and off the energy shell. The Born term in the expansion of the amplitude has the new feature that the vertices in the pole diagram are undressed, while those in the crossed, contact, and pion pole diagrams are dressed.
An Informal Overview of the Unitary Group Approach
Energy Technology Data Exchange (ETDEWEB)
Sonnad, V. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Escher, J. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Kruse, M. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Baker, R. [Louisiana State Univ., Baton Rouge, LA (United States). Dept. of Physics and Astronomy
2016-06-13
The Unitary Groups Approach (UGA) is an elegant and conceptually unified approach to quantum structure calculations. It has been widely used in molecular structure calculations, and holds the promise of a single computational approach to structure calculations in a variety of different fields. We explore the possibility of extending the UGA to computations in atomic and nuclear structure as a simpler alternative to traditional Racah algebra-based approaches. We provide a simple introduction to the basic UGA and consider some of the issues in using the UGA with spin-dependent, multi-body Hamiltonians requiring multi-shell bases adapted to additional symmetries. While the UGA is perfectly capable of dealing with such problems, it is seen that the complexity rises dramatically, and the UGA is not at this time, a simpler alternative to Racah algebra-based approaches.
C T for non-unitary CFTs in higher dimensions
Osborn, Hugh; Stergiou, Andreas
2016-06-01
The coefficient C T of the conformal energy-momentum tensor two-point function is determined for the non-unitary scalar CFTs with four- and six-derivative kinetic terms. The results match those expected from large- N calculations for the CFTs arising from the O( N) non-linear sigma and Gross-Neveu models in specific even dimensions. C T is also calculated for the CFT arising from ( n - 1)-form gauge fields with derivatives in 2 n + 2 dimensions. Results for ( n - 1)-form theory extended to general dimensions as a non-gauge-invariant CFT are also obtained; the resulting C T differs from that for the gauge-invariant theory. The construction of conformal primaries by subtracting descendants of lower-dimension primaries is also discussed. For free theories this also leads to an alternative construction of the energy-momentum tensor, which can be quite involved for higher-derivative theories.
The unitary conformal field theory behind 2D Asymptotic Safety
Nink, Andreas
2015-01-01
Being interested in the compatibility of Asymptotic Safety with Hilbert space positivity (unitarity), we consider a local truncation of the functional RG flow which describes quantum gravity in $d>2$ dimensions and construct its limit of exactly two dimensions. We find that in this limit the flow displays a nontrivial fixed point whose effective average action is a non-local functional of the metric. Its pure gravity sector is shown to correspond to a unitary conformal field theory with positive central charge $c=25$. Representing the fixed point CFT by a Liouville theory in the conformal gauge, we investigate its general properties and their implications for the Asymptotic Safety program. In particular, we discuss its field parametrization dependence and argue that there might exist more than one universality class of metric gravity theories in two dimensions. Furthermore, studying the gravitational dressing in 2D asymptotically safe gravity coupled to conformal matter we uncover a mechanism which leads to a...
Qubit Transport Model for Unitary Black Hole Evaporation without Firewalls
Osuga, Kento
2016-01-01
We give an explicit toy qubit transport model for transferring information from the gravitational field of a black hole to the Hawking radiation by a continuous unitary transformation of the outgoing radiation and the black hole gravitational field. The model has no firewalls or other drama at the event horizon and fits the set of six physical constraints that Giddings has proposed for models of black hole evaporation. It does utilize nonlocal qubits for the gravitational field but assumes that the radiation interacts locally with these nonlocal qubits, so in some sense the nonlocality is confined to the gravitational sector. Although the qubit model is too crude to be quantitively correct for the detailed spectrum of Hawking radiation, it fits qualitatively with what is expected.
Description and calibration of the Langley unitary plan wind tunnel
Jackson, C. M., Jr.; Corlett, W. A.; Monta, W. J.
1981-01-01
The two test sections of the Langley Unitary Plan Wind Tunnel were calibrated over the operating Mach number range from 1.47 to 4.63. The results of the calibration are presented along with a a description of the facility and its operational capability. The calibrations include Mach number and flow angularity distributions in both test sections at selected Mach numbers and tunnel stagnation pressures. Calibration data are also presented on turbulence, test-section boundary layer characteristics, moisture effects, blockage, and stagnation-temperature distributions. The facility is described in detail including dimensions and capacities where appropriate, and example of special test capabilities are presented. The operating parameters are fully defined and the power consumption characteristics are discussed.
Kitaev honeycomb tensor networks: Exact unitary circuits and applications
Schmoll, Philipp; Orús, Román
2017-01-01
The Kitaev honeycomb model is a paradigm of exactly solvable models, showing nontrivial physical properties such as topological quantum order, Abelian and non-Abelian anyons, and chirality. Its solution is one of the most beautiful examples of the interplay of different mathematical techniques in condensed matter physics. In this paper, we show how to derive a tensor network (TN) description of the eigenstates of this spin-1/2 model in the thermodynamic limit, and in particular for its ground state. In our setting, eigenstates are naturally encoded by an exact 3d TN structure made of fermionic unitary operators, corresponding to the unitary quantum circuit building up the many-body quantum state. In our derivation we review how the different "solution ingredients" of the Kitaev honeycomb model can be accounted for in the TN language, namely, Jordan-Wigner transformation, braidings of Majorana modes, fermionic Fourier transformation, and Bogoliubov transformation. The TN built in this way allows for a clear understanding of several properties of the model. In particular, we show how the fidelity diagram is straightforward both at zero temperature and at finite temperature in the vortex-free sector. We also show how the properties of two-point correlation functions follow easily. Finally, we also discuss the pros and cons of contracting of our 3d TN down to a 2d projected entangled pair state (PEPS) with finite bond dimension. The results in this paper can be extended to generalizations of the Kitaev model, e.g., to other lattices, spins, and dimensions.
Disordered complex systems using cold gases and trapped ions
De, A S; Lewenstein, M; Ahufinger, V; Pons, M L; Sanpera, A; De, Aditi Sen; Sen, Ujjwal; Lewenstein, Maciej; Ahufinger, Veronica; Pons, Marisa Ll.; Sanpera, Anna
2005-01-01
We report our research on disordered complex systems using cold gases and trapped ions, and address the possibility of using complex systems for quantum information processing. Two simple paradigmatic models of disordered complex systems are revisited here. The first one corresponds to a short range disordered Ising Hamiltonian (spin glasses), which can be implemented with a Bose-Fermi (Bose-Bose) mixture in a disordered optical lattice. The second model we address here is a long range disordered Hamiltonian, characteristic of neural networks (Hopfield model), which can be implemented in a chain of trapped ions with appropriately designed interactions.
Bioterrorism and the Fermi Paradox
Cooper, Joshua
2013-04-01
We proffer a contemporary solution to the so-called Fermi Paradox, which is concerned with conflict between Copernicanism and the apparent paucity of evidence for intelligent alien civilizations. In particular, we argue that every community of organisms that reaches its space-faring age will (1) almost immediately use its rocket-building computers to reverse-engineer its genetic chemistry and (2) self-destruct when some individual uses said technology to design an omnicidal pathogen. We discuss some of the possible approaches to prevention with regard to Homo sapiens' vulnerability to bioterrorism, particularly on a short-term basis.
Smirnov, Boris M
2001-01-01
A comprehensive textbook and reference for the study of the physics of ionized gasesThe intent of this book is to provide deep physical insight into the behavior of gases containing atoms and molecules from which one or more electrons have been ionized. The study of these so-called plasmas begins with an overview of plasmas as they are found in nature and created in the laboratory. This serves as a prelude to a comprehensive study of plasmas, beginning with low temperature and "ideal" plasmas and extending to radiation and particle transport phenomena, the response of plasmas to external fields, and an insightful treatment of plasma waves, plasma instabilities, nonlinear phenomena in plasmas, and the study of plasma interactions with surfaces
Energy Technology Data Exchange (ETDEWEB)
Clarke, R.
1987-01-01
The main greenhouse gases are carbon dioxide, methane, nitrous oxide, CFCs and ozone. They are greenhouse gases as they absorb radiation from the Earth and thus impede its emission back to space. CO{sub 2} is responsible for about half the enhanced greenhouse effect. A global warming of only a few degrees would have a profound effect on climate. Increased levels of CO{sub 2} promote plant growth, but may not benefit agriculture overall. Sea levels may rise. It is difficult to predict the effects of global warming in society. It would be possible to reduce the scale of the greenhouse effect by energy conservation, using alternative energy sources, and possibly by capturing CO{sub 2} from fossil fuel power stations and disposing of it on the ocean floor. 13 refs., 19 figs., 1 tab.
Alpay, D.; Dijksma, A.; Langer, H.
2004-01-01
We prove that a 2 × 2 matrix polynomial which is J-unitary on the real line can be written as a product of normalized elementary J-unitary factors and a J-unitary constant. In the second part we give an algorithm for this factorization using an analog of the Schur transformation.
Bi-directional modulation of AMPA receptor unitary conductance by synaptic activity
Directory of Open Access Journals (Sweden)
Matthews Paul
2004-11-01
Full Text Available Abstract Background Knowledge of how synapses alter their efficiency of communication is central to the understanding of learning and memory. The most extensively studied forms of synaptic plasticity are long-term potentiation (LTP and its counterpart long-term depression (LTD of AMPA receptor-mediated synaptic transmission. In the CA1 region of the hippocampus, it has been shown that LTP often involves a rapid increase in the unitary conductance of AMPA receptor channels. However, LTP can also occur in the absence of any alteration in AMPA receptor unitary conductance. In the present study we have used whole-cell dendritic recording, failures analysis and non-stationary fluctuation analysis to investigate the mechanism of depotentiation of LTP. Results We find that when LTP involves an increase in unitary conductance, subsequent depotentiation invariably involves the return of unitary conductance to pre-LTP values. In contrast, when LTP does not involve a change in unitary conductance then depotentiation also occurs in the absence of any change in unitary conductance, indicating a reduction in the number of activated receptors as the most likely mechanism. Conclusions These data show that unitary conductance can be bi-directionally modified by synaptic activity. Furthermore, there are at least two distinct mechanisms to restore synaptic strength from a potentiated state, which depend upon the mechanism of the previous potentiation.
Energy–pressure relation for low-dimensional gases
Directory of Open Access Journals (Sweden)
Francesco Mancarella
2014-10-01
Full Text Available A particularly simple relation of proportionality between internal energy and pressure holds for scale-invariant thermodynamic systems (with Hamiltonians homogeneous functions of the coordinates, including classical and quantum – Bose and Fermi – ideal gases. One can quantify the deviation from such a relation by introducing the internal energy shift as the difference between the internal energy of the system and the corresponding value for scale-invariant (including ideal gases. After discussing some general thermodynamic properties associated with the scale-invariance, we provide criteria for which the internal energy shift density of an imperfect (classical or quantum gas is a bounded function of temperature. We then study the internal energy shift and deviations from the energy–pressure proportionality in low-dimensional models of gases interpolating between the ideal Bose and the ideal Fermi gases, focusing on the Lieb–Liniger model in 1d and on the anyonic gas in 2d. In 1d the internal energy shift is determined from the thermodynamic Bethe ansatz integral equations and an explicit relation for it is given at high temperature. Our results show that the internal energy shift is positive, it vanishes in the two limits of zero and infinite coupling (respectively the ideal Bose and the Tonks–Girardeau gas and it has a maximum at a finite, temperature-depending, value of the coupling. Remarkably, at fixed coupling the energy shift density saturates to a finite value for infinite temperature. In 2d we consider systems of Abelian anyons and non-Abelian Chern–Simons particles: as it can be seen also directly from a study of the virial coefficients, in the usually considered hard-core limit the internal energy shift vanishes and the energy is just proportional to the pressure, with the proportionality constant being simply the area of the system. Soft-core boundary conditions at coincident points for the two-body wavefunction introduce
On the theory of polarized Fermi liquid
Mineev, V. P.
2004-01-01
The transport equation for transverse vibrations of magnetization in spin polarized Fermi liquid is derived from integral equation for the vertex function. The dispersion law for the transverse spin waves is established. The existance of zero-temperature spin-waves attenuation is confirmed. The problem of similar derivation in ferromagnetic "Fermi liquid" is discussed.
Fermi Surface and Antiferromagnetism in Europium Metal
DEFF Research Database (Denmark)
Andersen, O. Krogh; Loucks, T. L.
1968-01-01
We have calculated the Fermi surface of europium in order to find those features which determine the wave vector of the helical moment arrangement below the Néel point. We find that there are two pieces of Fermi surface: an electron surface at the symmetry point H, which has the shape of rounded-...
The Fermi paradox and coronary artery disease
National Research Council Canada - National Science Library
Gottlieb, Ilan; Lima, Ronaldo Souza Leão
2014-01-01
..., led Fermi to ask the famous question: "Where is everybody?" Fermi was confronted with a paradox that involved probability, scale, and evidence. Coronary artery disease (CAD) presents a similar challenge. The pathophysiological importance of nonobstructive CAD is well known, as two-thirds of acute coronary syndromes (ACS) originate...
Vacuum alignment and radiatively induced Fermi scale
Alanne, Tommi
2016-01-01
We extend the discussion about vacuum misalignment by quantum corrections in models with composite pseudo-Goldstone Higgs boson to renormalisable models with elementary scalars. As a concrete example, we propose a framework, where the hierarchy between the unification and the Fermi scale emerges radiatively. This scenario provides an interesting link between the unification and Fermi scale physics.
Enrico Fermi significato di una scoperta
2001-01-01
Questo volume è la riedizione, rinnovata ed ampliata, del volume "Enrico Fermi. Significato di una scoperta" edito dal FIEN (Forum Italiano dell'Energia Nucleare) nel 1982 e nel 1992 in occasione, rispettivamente, del 40mo e del 50mo anniversario della pila di Fermi.
Unitary theories in the work of Mira Fernandes (beyond general relativity and differential geometry)
Lemos, José P S
2010-01-01
An analysis of the work of Mira Fernandes on unitary theories is presented. First it is briefly mentioned the Portuguese scientific context of the 1920s. A short analysis of the extension of Riemann geometries to new generalized geometries with new affine connections, such as those of Weyl and Cartan, is given. Based on these new geometries, the unitary theories of the gravitational and electromagnetic fields, proposed by Weyl, Eddington, Einstein, and others are then explained. Finally, the book and one paper on connections and two papers on unitary theories, all written by Mira Fernandes, are analyzed and put in context.
[Reactualization of the concept of unitary psychosis introduced by Joseph Guislain].
van Renynghe de Voxvrie, G
1993-01-01
This paper reminds the concept of a unitary nosological and pathogenic process that may be traced back to Joseph Guislain (1797-1860). The "phrénalgie initiale" was regarded as the initial stage of psychic illness by Guislain (Leçons orales, Ghent, 1852). That vision inspired the work of Wilhelm Griesinger (1817-1869) who further elaborated the concept of "Einheitspsychose" (Psychose unique--Unitary psychosis). That concept partially inspired Emil Kräpelin (1856-1926). Current classification systems like ICD-10 and DSM-III-R attempt to synthesize different views and the concept of unitary psychosis is actualized in the contemporary transnosography.
Participatory dreaming: a conceptual exploration from a unitary appreciative inquiry perspective.
Repede, Elizabeth J
2009-10-01
Dreaming is a universal phenomenon in human experience and one that carries multiple meanings in the narrative discourse across disciplines. Dreams can be collective, communal, and emancipatory, as well as individual. While individual dreaming has been extensively studied in the literature, the participatory nature of dreaming as a unitary phenomenon is limited. The concept of participatory dreaming within a unitary appreciative framework for healing is explored from perspectives in anthropology, psychology, and nursing. A participatory model of dreaming is proposed from a synthesis of the literature for use in future research using unitary appreciative inquiry.
Participatory dreaming: a unitary appreciative inquiry into healing with women abused as children.
Repede, Elizabeth
2011-01-01
Unitary appreciative inquiry was used to explore healing in the lives of 11 women abused as children using a model of participatory dreaming. Aesthetics, imagery, and journaling were used in a participatory design aimed at the appreciation of healing in the lives of the participants as it related to the abuse. Using Cowling's theory of unitary healing, research and practice were combined within a unitary-transformative framework. Participatory dreaming was useful in illuminating the life patterning in the lives of the women and promoted the development of new knowledge and skills that led to change and transformation, both individually and collectively.
Biased discrete symmetry breaking and Fermi balls
MacPherson, A L; Macpherson, Alick L; Campbell, Bruce A
1994-01-01
The spontaneous breaking of an approximate discrete symmetry is considered, with the resulting protodomains of true and false vacuum being separated by domain walls. Given a strong, symmetric Yukawa coupling of the real scalar field to a generic fermion, the domain walls accumulate a gas of fermions, which modify the domain wall dynamics. The splitting of the degeneracy of the ground states results in the false vacuum protodomain structures eventually being fragmented into tiny false vacuum bags with a Fermi gas shell (Fermi balls), that may be cosmologically stable due to the Fermi gas pressure and wall curvature forces, acting on the domain walls. As fermions inhabiting the domain walls do not undergo number density freeze out, stable Fermi balls exist only if a fermion anti-fermion asymmetry occurs. Fermi balls formed with a new Dirac fermion that possesses no standard model gauge charges provide a novel cold dark matter candidate.
N. Fabbri; M. Panfil; D. Clément; L. Fallani; M. Inguscio; C. Fort; J.-S. Caux
2015-01-01
Interactions are known to have dramatic effects on bosonic gases in one dimension (1D). Not only does the ground state transform from a condensate like state to an effective Fermi sea, but new fundamental excitations, which do not have any higher-dimensional equivalents, are predicted to appear. In
Directory of Open Access Journals (Sweden)
Laurent Chusseau
2013-02-01
Full Text Available We show that the thermodynamics of ideal gases may be derived solely from the Democritean concept of corpuscles moving in vacuum plus a principle of simplicity, namely that these laws are independent of the laws of motion, aside from the law of energy conservation. Only a single corpuscle in contact with a heat bath submitted to a z and t-invariant force is considered. Most of the end results are known but the method appears to be novel. The mathematics being elementary, the present paper should facilitate the understanding of the ideal gas law and of classical thermodynamics even though not-usually-taught concepts are being introduced.
Deformations of Polyhedra and Polygons by the Unitary Group
Livine, Etera R
2013-01-01
We introduce the set of framed convex polyhedra with N faces as the symplectic quotient C^2N//SU(2). A framed polyhedron is then parametrized by N spinors living in C^2 satisfying suitable closure constraints and defines a usual convex polyhedron plus a phase for each face. We show that there is an action of the unitary group U(N) on this phase space, which changes the shape of faces and allows to map any polyhedron onto any other with the same total area. This realizes the isomorphism of the space of framed polyhedra with the Grassmannian space U(N)/SU(2)*U(N-2). We show how to write averages and correlations of geometrical observables over the ensemble of polyhedra as polynomial integrals over U(N) and we use the Itzykson-Zuber formula from matrix models as the generating function for them. In the quantum case, a canonical quantization of the framed polyhedron phase space leads to the Hilbert space of SU(2) intertwiners. The individual face areas are quantized as half-integers (spins) and the Hilbert spaces...
Unitary Networks from the Exact Renormalization of Wave Functionals
Fliss, Jackson R; Parrikar, Onkar
2016-01-01
The exact renormalization group (ERG) for $O(N)$ vector models (at large $N$) on flat Euclidean space can be interpreted as the bulk dynamics corresponding to a holographically dual higher spin gauge theory on $AdS_{d+1}$. This was established in the sense that at large $N$ the generating functional of correlation functions of single trace operators is reproduced by the on-shell action of the bulk higher spin theory, which is most simply presented in a first-order (phase space) formalism. In this paper, we extend the ERG formalism to the wave functionals of arbitrary states of the $O(N)$ vector model at the free fixed point. We find that the ERG flow of the ground state and a specific class of excited states is implemented by the action of unitary operators which can be chosen to be local. Consequently, the ERG equations provide a continuum notion of a tensor network. We compare this tensor network with the entanglement renormalization networks, MERA, and its continuum version, cMERA, which have appeared rece...
Renormalization of the unitary evolution equation for coined quantum walks
Boettcher, Stefan; Li, Shanshan; Portugal, Renato
2017-03-01
We consider discrete-time evolution equations in which the stochastic operator of a classical random walk is replaced by a unitary operator. Such a problem has gained much attention as a framework for coined quantum walks that are essential for attaining the Grover limit for quantum search algorithms in physically realizable, low-dimensional geometries. In particular, we analyze the exact real-space renormalization group (RG) procedure recently introduced to study the scaling of quantum walks on fractal networks. While this procedure, when implemented numerically, was able to provide some deep insights into the relation between classical and quantum walks, its analytic basis has remained obscure. Our discussion here is laying the groundwork for a rigorous implementation of the RG for this important class of transport and algorithmic problems, although some instances remain unresolved. Specifically, we find that the RG fixed-point analysis of the classical walk, which typically focuses on the dominant Jacobian eigenvalue {λ1} , with walk dimension dw\\text{RW}={{log}2}{λ1} , needs to be extended to include the subdominant eigenvalue {λ2} , such that the dimension of the quantum walk obtains dw\\text{QW}={{log}2}\\sqrt{{λ1}{λ2}} . With that extension, we obtain analytically previously conjectured results for dw\\text{QW} of Grover walks on all but one of the fractal networks that have been considered.
Unitary fermions and Lüscher's formula on a crystal
Valiente, Manuel; Zinner, Nikolaj T.
2016-11-01
We consider the low-energy particle-particle scattering properties in a periodic simple cubic crystal. In particular, we investigate the relation between the two-body scattering length and the energy shift experienced by the lowest-lying unbound state when this is placed in a periodic finite box. We introduce a continuum model for s-wave contact interactions that respects the symmetry of the Brillouin zone in its regularisation and renormalisation procedures, and corresponds to the naïve continuum limit of the Hubbard model. The energy shifts are found to be identical to those obtained in the usual spherically symmetric renormalisation scheme upon resolving an important subtlety regarding the cutoff procedure. We then particularize to the Hubbard model, and find that for large finite lattices the results are identical to those obtained in the continuum limit. The results reported here are valid in the weak, intermediate and unitary limits. These may be used to significantly ease the extraction of scattering information, and therefore effective interactions in condensed matter systems in realistic periodic potentials. This can achieved via exact diagonalisation or Monte Carlo methods, without the need to solve challenging, genuine multichannel collisional problems with very restricted symmetry simplifications.
Conditional Mutual Information of Bipartite Unitaries and Scrambling
Ding, Dawei; Walter, Michael
2016-01-01
One way to diagnose chaos in bipartite unitary channels is via the negativity of the tripartite information of the corresponding Choi state, which for certain choices of the subsystems reduces to the negative conditional mutual information (CMI). We study this quantity from a quantum information-theoretic perspective to clarify its role in diagnosing scrambling. When the CMI is zero, we find that the channel has a special normal form consisting of local channels between individual inputs and outputs. However, we find that arbitrarily low CMI does not imply arbitrary proximity to a channel of this form, although it does imply a type of approximate recoverability of one of the inputs. When the CMI is maximal, we find that the residual channel from an individual input to an individual output is completely depolarizing when the other inputs are maximally mixed. However, we again find that this result is not robust. We also extend some of these results to the multipartite case and to the case of Haar-random pure i...
On the infinite fern of Galois representations of unitary type
Chenevier, Gaetan
2009-01-01
Let E be a CM number field, F its maximal totally real subfield, c the generator of Gal(E/F), p an odd prime totally split in E, and S a finite set of places of E containing the places above p. Let r : G_{E,S} --> GL_3(F_p^bar) be a modular, absolutely irreducible, Galois representation of type U(3), i.e. such that r^* = r^c, and let X(r) be the rigid analytic generic fiber of its universal G_{E,S}-deformation of type U(3). We show that each irreducible component of the Zariski-closure of the modular points in X(r) has dimension at least 6[F:Q]. We study an analogue of the infinite fern of Gouvea-Mazur in this context and deal with the Hilbert modular case as well. As important steps, we prove that any first order deformation of a generic enough crystalline representation of Gal(Q_p^bar/Q_p) (of any dimension) is a linear combination of trianguline deformations, and that unitary eigenvarieties (of any rank) are etale over the weight space at the non-critical classical points. As another application, we obtain...
Holographic Fluctuations from Unitary de Sitter Invariant Field Theory
Banks, Tom; Torres, T J; Wainwright, Carroll L
2013-01-01
We continue the study of inflationary fluctuations in Holographic Space Time models of inflation. We argue that the holographic theory of inflation provides a physical context for what is often called dS/CFT. The holographic theory is a quantum theory which, in the limit of a large number of e-foldings, gives rise to a field theory on $S^3$, which is the representation space for a unitary representation of SO(1,4). This is not a conventional CFT, and we do not know the detailed non-perturbative axioms for correlation functions. However, the two- and three-point functions are completely determined by symmetry, and coincide up to a few constants (really functions of the background FRW geometry) with those calculated in a single field slow-roll inflation model. The only significant deviation from slow roll is in the tensor fluctuations. We predict zero tensor tilt and roughly equal weight for all three conformally invariant tensor 3-point functions (unless parity is imposed as a symmetry). We discuss the relatio...
Spectral Characteristics of the Unitary Critical Almost-Mathieu Operator
Fillman, Jake; Ong, Darren C.; Zhang, Zhenghe
2016-10-01
We discuss spectral characteristics of a one-dimensional quantum walk whose coins are distributed quasi-periodically. The unitary update rule of this quantum walk shares many spectral characteristics with the critical Almost-Mathieu Operator; however, it possesses a feature not present in the Almost-Mathieu Operator, namely singularity of the associated cocycles (this feature is, however, present in the so-called Extended Harper's Model). We show that this operator has empty absolutely continuous spectrum and that the Lyapunov exponent vanishes on the spectrum; hence, this model exhibits Cantor spectrum of zero Lebesgue measure for all irrational frequencies and arbitrary phase, which in physics is known as Hofstadter's butterfly. In fact, we will show something stronger, namely, that all spectral parameters in the spectrum are of critical type, in the language of Avila's global theory of analytic quasiperiodic cocycles. We further prove that it has empty point spectrum for each irrational frequency and away from a frequency-dependent set of phases having Lebesgue measure zero. The key ingredients in our proofs are an adaptation of Avila's Global Theory to the present setting, self-duality via the Fourier transform, and a Johnson-type theorem for singular dynamically defined CMV matrices which characterizes their spectra as the set of spectral parameters at which the associated cocycles fail to admit a dominated splitting.
Rooftop Unitary Air Conditioner with Integral Dedicated Outdoor Air System
Energy Technology Data Exchange (ETDEWEB)
Tiax Llc
2006-02-28
Energy use of rooftop and other unitary air-conditioners in commercial applications accounts for about 1 quad (10{sup 15} Btu) of primary energy use annually in the U.S. [Reference 7]. The realization that this cooling equipment accounts for the majority of commercial building cooled floorspace and the majority also of commercial building energy use has spurred development of improved-efficiency equipment as well as development of stricter standards addressing efficiency levels. Another key market driver affecting design of rooftop air-conditioning equipment has been concern regarding comfort and the control of humidity. Trends for increases in outdoor air ventilation rates in certain applications, and the increasing concern about indoor air quality problems associated with humidity levels and moisture in buildings points to a need for improved dehumidification capability in air-conditioning equipment of all types. In many cases addressing this issue exacerbates energy efficiency, and vice versa. The integrated dedicated outdoor air system configuration developed in this project addresses both energy and comfort/humidity issues.
Energy Technology Data Exchange (ETDEWEB)
Akibue, Seiseki [Department of Physics, Graduate School of Science, The University of Tokyo, Tokyo (Japan); Murao, Mio [Department of Physics, Graduate School of Science, The University of Tokyo, Tokyo, Japan and NanoQuine, The University of Tokyo, Tokyo (Japan)
2014-12-04
We investigate distributed implementation of two-qubit unitary operations over two primitive networks, the butterfly network and the ladder network, as a first step to apply network coding for quantum computation. By classifying two-qubit unitary operations in terms of the Kraus-Cirac number, the number of non-zero parameters describing the global part of two-qubit unitary operations, we analyze which class of two-qubit unitary operations is implementable over these networks with free classical communication. For the butterfly network, we show that two classes of two-qubit unitary operations, which contain all Clifford, controlled-unitary and matchgate operations, are implementable over the network. For the ladder network, we show that two-qubit unitary operations are implementable over the network if and only if their Kraus-Cirac number do not exceed the number of the bridges of the ladder.
Reiss, Howard R.; Smirnov, Boris M.
2001-03-01
A comprehensive textbook and reference for the study of the physics of ionized gases The intent of this book is to provide deep physical insight into the behavior of gases containing atoms and molecules from which one or more electrons have been ionized. The study of these so-called plasmas begins with an overview of plasmas as they are found in nature and created in the laboratory. This serves as a prelude to a comprehensive study of plasmas, beginning with low temperature and "ideal" plasmas and extending to radiation and particle transport phenomena, the response of plasmas to external fields, and an insightful treatment of plasma waves, plasma instabilities, nonlinear phenomena in plasmas, and the study of plasma interactions with surfaces. In all cases, the emphasis is on a clear and unified understanding of the basic physics that underlies all plasma phenomena. Thus, there are chapters on plasma behavior from the viewpoint of atomic and molecular physics, as well as on the macroscopic phenomena involved in physical kinetics of plasmas and the transport of radiation and of charged particles within plasmas. With this grounding in the fundamental physics of plasmas, the notoriously difficult subjects of nonlinear phenomena and of instabilities in plasmas are then treated with comprehensive clarity.
Unitary background gauges and hamiltonian approach to Yang-Mills theories
Dubin, A Yu
1995-01-01
A variety of unitary gauges for perturbation theory in a background field is considered in order to find those most suitable for a Hamiltonian treatment of the system. We select two convenient gauges and derive the propagators D_{\\mu\
Error correcting codes for binary unitary channels on multipartite quantum systems
Choi, M D; Kribs, D W; Zyczkowski, K; Choi, Man-Duen; Holbrook, John A.; Kribs, David W.; Zyczkowski, Karol
2006-01-01
We conduct an analysis of ideal error correcting codes for randomized unitary channels determined by two unitary error operators -- what we call ``binary unitary channels'' -- on multipartite quantum systems. In a wide variety of cases we give a complete description of the code structure for such channels. Specifically, we find a practical geometric technique to determine the existence of codes of arbitrary dimension, and then derive an explicit construction of codes of a given dimension when they exist. For instance, given any binary unitary noise model on an n-qubit system, we design codes that support n-2 qubits. We accomplish this by verifying a conjecture for higher rank numerical ranges of normal operators in many cases.
Palao, J P; Palao, Jose P.; Kosloff, Ronnie
2002-01-01
A quantum gate is realized by specific unitary transformations operating on states representing qubits. Considering a quantum system employed as an element in a quantum computing scheme, the task is therefore to enforce the pre-specified unitary transformation. This task is carried out by an external time dependent field. Optimal control theory has been suggested as a method to compute the external field which alters the evolution of the system such that it performs the desire unitary transformation. This study compares two recent implementations of optimal control theory to find the field that induces a quantum gate. The first approach is based on the equation of motion of the unitary transformation. The second approach generalizes the state to state formulation of optimal control theory. This work highlight the formal relation between the two approaches.
Matrix Elements of One- and Two-Body Operators in the Unitary Group Approach (II) - Application
Institute of Scientific and Technical Information of China (English)
DAI Lian-Rong; PAN Feng
2001-01-01
Simple analytical expressions for one- and two-body matrix elements in the unitary group approach to the configuration interaction problems of many-electron systems are obtained based on the previous results for general Un irreps.
Institute of Scientific and Technical Information of China (English)
FAN Hong-Yi; HU Shan
2006-01-01
We present a general formalism for setting up unitary transform operators from classical transforms via the technique of integration within an ordered product of operators, their normally ordered form can be obtained too.
Can a non-unitary effect be prominent In neutrino oscillation measurements?
Institute of Scientific and Technical Information of China (English)
L(U) Lei; WANG Wen-Yu; XIONG zhao-Hua
2010-01-01
Subject to neutrino experiments, the mixing matrix of ordinary neutrinos can still have small vi-olation from unitarity. We introduce a quasi-unitary matrix to interpret this violation and propose a natural scheme to parameterize it. A quasi-unitary factor △QF is defined to be measured in neutrino oscillation exper-iments and the numerical results show that the improvement in experimental precision may help us figure out the secret of neutrino mixing.
Directory of Open Access Journals (Sweden)
Chau Hoi
2011-01-01
Full Text Available Abstract We give elementary proofs of two theorems concerning bounds on the maximum argument of the eigenvalues of a product of two unitary matrices--one by Childs et al. [J. Mod. Phys. 47, 155 (2000] and the other one by Chau [Quant. Inf. Comp. 11, 721 (2011]. Our proofs have the advantages that the necessary and sufficient conditions for equalities are apparent and that they can be readily generalized to the case of infinite-dimensional unitary operators.
Branching laws for small unitary representations of GL(n,C)
DEFF Research Database (Denmark)
Möllers, Jan; Schwarz, Benjamin
2014-01-01
The unitary principal series representations of $G=GL(n,\\mathbb{C})$ induced from a character of the maximal parabolic subgroup $P=(GL(1,\\mathbb{C})\\times GL(n-1,\\mathbb{C}))\\ltimes\\mathbb{C}^{n-1}$ attain the minimal Gelfand--Kirillov dimension among all infinite-dimensional unitary representati...... representations of $G$. We find the explicit branching laws for the restriction of these representations to symmetric subgroups of $G$....
Quantum chaos on a critical Fermi surface
Patel, Aavishkar A
2016-01-01
We compute parameters characterizing many-body quantum chaos for a critical Fermi surface without quasiparticle excitations. We examine a theory of $N$ species of fermions at non-zero density coupled to a $U(1)$ gauge field in two spatial dimensions, and determine the Lyapunov rate and the butterfly velocity in an extended RPA approximation. The thermal diffusivity is found to be universally related to these chaos parameters, i.e. the relationship is independent of $N$, the gauge coupling constant, the Fermi velocity, the Fermi surface curvature, and high energy details.
Fermi polaron-polaritons in charge-tunable atomically thin semiconductors
Sidler, Meinrad; Back, Patrick; Cotlet, Ovidiu; Srivastava, Ajit; Fink, Thomas; Kroner, Martin; Demler, Eugene; Imamoglu, Atac
2017-03-01
The dynamics of a mobile quantum impurity in a degenerate Fermi system is a fundamental problem in many-body physics. The interest in this field has been renewed due to recent ground-breaking experiments with ultracold Fermi gases. Optical creation of an exciton or a polariton in a two-dimensional electron system embedded in a microcavity constitutes a new frontier for this field due to an interplay between cavity coupling favouring ultralow-mass polariton formation and exciton-electron interactions leading to polaron or trion formation. Here, we present cavity spectroscopy of gate-tunable monolayer MoSe2 (ref. ) exhibiting strongly bound trion and polaron resonances, as well as non-perturbative coupling to a single microcavity mode. As the electron density is increased, the oscillator strength determined from the polariton splitting is gradually transferred from the higher-energy repulsive exciton-polaron resonance to the lower-energy attractive exciton-polaron state. Simultaneous observation of polariton formation in both attractive and repulsive branches indicates a new regime of polaron physics where the polariton impurity mass can be much smaller than that of the electrons. Our findings shed new light on optical response of semiconductors in the presence of free carriers by identifying the Fermi polaron nature of excitonic resonances and constitute a first step in investigation of a new class of degenerate Bose-Fermi mixtures.
Higher-nodal collective modes in a resonantly interacting Fermi gas
Guajardo, Edmundo R. Sánchez; Tey, Meng Khoon; Sidorenkov, Leonid A.; Grimm, Rudolf
2013-06-01
We report on experimental investigations of longitudinal collective oscillations in a highly elongated, harmonically trapped two-component Fermi gas with resonantly tuned s-wave interactions (“unitary Fermi gas”). We focus on higher-nodal axial modes, which in contrast to the elementary modes have received little attention so far. We show how these modes can be efficiently excited using a resonant local excitation scheme and sensitively analyzed by a Fourier transformation of the detected time evolution of the axial density profile. We study the temperature dependence of the mode frequencies across the superfluid phase transition. The behavior is qualitatively different from the elementary modes, where the mode frequencies are independent of the temperature as long as the gas stays in the hydrodynamic regime. Our results are compared to theoretical predictions based on Landau's two-fluid theory and available experimental knowledge of the equation of state. The comparison shows excellent agreement and thus both represents a sensitive test for the validity of the theoretical approach and provides an independent test of the equation of state. The present results obtained on modes of first-sound character represent benchmarks for the observation of second-sound propagation and corresponding oscillation modes.
Deep inelastic scattering on ultracold gases
Hofmann, Johannes
2016-01-01
We discuss the dynamic structure factor of both Bose and Fermi gases with strong short-range interactions, focussing on the deep inelastic regime of large wave vector transfer $q$. Here, the dynamic structure factor is dominated by a resonance at the free-particle energy $\\hbar \\omega = \\varepsilon_{\\bf q} = \\hbar^2 q^2/2m$ and is described in terms of scaling functions. We show that the high-momentum structure has a rich scaling behavior characterized by two separate scaling regions: first, for frequencies that differ from the single-particle energy by terms of order ${\\cal O}(q)$ (i.e., small deviations compared to the single-particle energy), the dynamic structure factor is described by the impulse approximation (IA) of Hohenberg and Platzman. Second, deviations of order ${\\cal O}(q^2)$ (i.e., of the same order or larger than the single-particle energy) are described by the operator product expansion (OPE), with a universal cross-over connecting both regimes. We use the full asymptotic form to derive vario...
Signals of Bose Einstein condensation and Fermi quenching in the decay of hot nuclear systems
Directory of Open Access Journals (Sweden)
P. Marini
2016-05-01
Full Text Available We report on first experimental observations of nuclear fermionic and bosonic components displaying different behaviours in the decay of hot Ca projectile-like sources produced in mid-peripheral collisions at sub-Fermi energies. The experimental setup, constituted by the coupling of the INDRA 4π detector array to the forward angle VAMOS magnetic spectrometer, allowed to reconstruct the mass, charge and excitation energy of the decaying hot projectile-like sources. By means of quantum-fluctuation analysis techniques, temperatures and local partial densities of bosons and fermions could be correlated to the excitation energy of the reconstructed system. The results are consistent with the production of dilute mixed systems of bosons and fermions, where bosons experience higher phase-space and energy density as compared to the surrounding fermionic gas. Our findings recall phenomena observed in the study of Bose condensates and Fermi gases in atomic traps despite the different scales.
Radiatively induced Fermi scale and unification
Alanne, Tommi
2016-01-01
We propose a framework, where the hierarchy between the unification and the Fermi scale emerges radiatively. This work tackles the long-standing question about the connection between the low Fermi scale and a more fundamental scale of Nature. As a concrete example, we study a Pati-Salam-type unification of Elementary-Goldstone-Higgs scenario, where the Standard Model scalar sector is replaced by an SU(4)-symmetric one, and the observed Higgs particle is an elementary pseudo-Goldstone boson. We construct a concrete model where the unification scale is fixed to a phenomenologically viable value, while the Fermi scale is generated radiatively. This scenario provides an interesting link between the unification and Fermi scale physics, and opens up prospects for exploring a wide variety of open problems in particle physics, ranging from neutrinos to cosmic inflation.
Fermi: physicist with a capital F
Cobal, Marina
2016-12-01
Enrico Fermi – one of the great physicists of the 21st century – was a beacon for every Italian student of physics. This is wonderfully captured in The Pope of Physics by Gino Segrè and Bettina Hoerlin.
Fermi Surface of the Most Dilute Superconductor
Lin, Xiao; Zhu, Zengwei; Fauqué, Benoît; Behnia, Kamran
2013-04-01
The origin of superconductivity in bulk SrTiO3 is a mystery since the nonmonotonous variation of the critical transition with carrier concentration defies the expectations of the crudest version of the BCS theory. Here, employing the Nernst effect, an extremely sensitive probe of tiny bulk Fermi surfaces, we show that, down to concentrations as low as 5.5×1017cm-3, the system has both a sharp Fermi surface and a superconducting ground state. The most dilute superconductor currently known therefore has a metallic normal state with a Fermi energy as little as 1.1 meV on top of a band gap as large as 3 eV. The occurrence of a superconducting instability in an extremely small, single-component, and barely anisotropic Fermi surface implies strong constraints for the identification of the pairing mechanism.
Gamma-Ray Astrophysics NSSTC Fermi GBM
National Aeronautics and Space Administration — The Fermi Gamma-Ray Burst Monitor (GBM) is not a pointed or imaging instrument. To determine fluxes for known sources, we measure the change in the count rate...
Fermi's Conundrum: Proliferation and Closed Societies
Teller, Wendy; Westfall, Catherine
2007-04-01
On January 1, 1946 Emily Taft Douglas, a freshman Representative at Large for Illinois, sent a letter to Enrico Fermi. She wanted to know whether, if atomic energy was used for peaceful purposes, it might be possible to clandestinely divert some material for bombs. Douglas first learned about the bomb not quite five months before when Hiroshima was bombed. Even though she was not a scientist she identified a key problem of the nuclear age. Fermi responded with requirements to allow peaceful uses of atomic energy and still outlaw nuclear weapons. First, free interchange of information between people was required, and second, people who reported possible violations had to be protected. Fermi had lived in Mussolini's Italy and worked under the war time secrecy restrictions of the Manhattan Project. He was not optimistic that these conditions could be met. This paper discusses how Douglas came to recognize the proliferation issue and what led Fermi to his solution and his pessimism about its practicality.
A fast algorithm for finding point sources in the Fermi data stream: FermiFAST
Asvathaman, Asha; Omand, Conor; Barton, Alistair; Heyl, Jeremy S.
2017-04-01
We present a new and efficient algorithm for finding point sources in the photon event data stream from the Fermi Gamma-Ray Space Telescope, FermiFAST. The key advantage of FermiFAST is that it constructs a catalogue of potential sources very fast by arranging the photon data in a hierarchical data structure. Using this structure, FermiFAST rapidly finds the photons that could have originated from a potential gamma-ray source. It calculates a likelihood ratio for the contribution of the potential source using the angular distribution of the photons within the region of interest. It can find within a few minutes the most significant half of the Fermi Third Point Source catalogue (3FGL) with nearly 80 per cent purity from the 4 yr of data used to construct the catalogue. If a higher purity sample is desirable, one can achieve a sample that includes the most significant third of the Fermi 3FGL with only 5 per cent of the sources unassociated with Fermi sources. Outside the Galactic plane, all but eight of the 580 FermiFAST detections are associated with 3FGL sources. And of these eight, six yield significant detections of greater than 5σ when a further binned likelihood analysis is performed. This software allows for rapid exploration of the Fermi data, simulation of the source detection to calculate the selection function of various sources and the errors in the obtained parameters of the sources detected.
Coexistence of Fermi arcs and Fermi pockets in a high-T(c) copper oxide superconductor.
Meng, Jianqiao; Liu, Guodong; Zhang, Wentao; Zhao, Lin; Liu, Haiyun; Jia, Xiaowen; Mu, Daixiang; Liu, Shanyu; Dong, Xiaoli; Zhang, Jun; Lu, Wei; Wang, Guiling; Zhou, Yong; Zhu, Yong; Wang, Xiaoyang; Xu, Zuyan; Chen, Chuangtian; Zhou, X J
2009-11-19
In the pseudogap state of the high-transition-temperature (high-T(c)) copper oxide superconductors, angle-resolved photoemission (ARPES) measurements have seen Fermi arcs-that is, open-ended gapless sections in the large Fermi surface-rather than a closed loop expected of an ordinary metal. This is all the more puzzling because Fermi pockets (small closed Fermi surface features) have been suggested by recent quantum oscillation measurements. The Fermi arcs cannot be understood in terms of existing theories, although there is a solution in the form of conventional Fermi surface pockets associated with competing order, but with a back side that is for detailed reasons invisible to photoemission probes. Here we report ARPES measurements of Bi(2)Sr(2-x)La(x)CuO(6+delta) (La-Bi2201) that reveal Fermi pockets. The charge carriers in the pockets are holes, and the pockets show an unusual dependence on doping: they exist in underdoped but not overdoped samples. A surprise is that these Fermi pockets appear to coexist with the Fermi arcs. This coexistence has not been expected theoretically.
Conoscere Fermi nel centenario della nascita : 29 settembre 1901 - 2001
Bonolis, Luisa
2001-01-01
Il lavoro scientifico di Fermi riguarda molti campi disparati, ciascuno dei quali ha avuto uno sviluppo peculiare in tempi successivi alla morte. In questo volume un certo numero di specialisti contemporanei di ciascun settore espone in forma semplice l'idea originaria e la sua successiva evoluzione. INDICE. Carlo Bernardini, "Introduzione"; Giorgio Salvini, "Enrico Fermi. La sua vita, ed un commento alla sua opera"; Edoardo Amaldi, "Commemorazione del Socio Enrico Fermi"; Enrico Persico, "Commemorazione di Enrico Fermi"; Franco Rasetti, "Enrico Fermi e la Fisica Italiana"; Franco Bassani, "Enrico Fermi e la Fisica dello Stato Solido"; Giorgio Parisi, "La statistica di Fermi"; Giovanni Gallavotti, "La meccanica classica e la rivoluzione quantistica nei lavori giovanili di Fermi"; Tullio Levi-Civita, "Sugli invarianti adiabatici"; Bruno Bertotti, "Le coordinate di Fermi e il Principio di Equivalenza"; Marcello Cini, "Fermi e l'elettrodinamica quantistica"; Nicola Cabibbo. "Le interazioni deboli"; Ugo Amaldi, "...
Fermi breakup and the statistical multifragmentation model
Energy Technology Data Exchange (ETDEWEB)
Carlson, B.V., E-mail: brett@ita.br [Departamento de Fisica, Instituto Tecnologico de Aeronautica - CTA, 12228-900 Sao Jose dos Campos (Brazil); Donangelo, R. [Instituto de Fisica, Universidade Federal do Rio de Janeiro, Cidade Universitaria, CP 68528, 21941-972, Rio de Janeiro (Brazil); Instituto de Fisica, Facultad de Ingenieria, Universidad de la Republica, Julio Herrera y Reissig 565, 11.300 Montevideo (Uruguay); Souza, S.R. [Instituto de Fisica, Universidade Federal do Rio de Janeiro, Cidade Universitaria, CP 68528, 21941-972, Rio de Janeiro (Brazil); Instituto de Fisica, Universidade Federal do Rio Grande do Sul, Av. Bento Goncalves 9500, CP 15051, 91501-970, Porto Alegre (Brazil); Lynch, W.G.; Steiner, A.W.; Tsang, M.B. [Joint Institute for Nuclear Astrophysics, National Superconducting Cyclotron Laboratory and the Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States)
2012-02-15
We demonstrate the equivalence of a generalized Fermi breakup model, in which densities of excited states are taken into account, to the microcanonical statistical multifragmentation model used to describe the disintegration of highly excited fragments of nuclear reactions. We argue that such a model better fulfills the hypothesis of statistical equilibrium than the Fermi breakup model generally used to describe statistical disintegration of light mass nuclei.
Fermi-Dirac Statistics of Complex Networks
Institute of Scientific and Technical Information of China (English)
SHEN Yi; ZHU Di-Ling; LIU Wei-Ming
2005-01-01
@@ We investigate phenomena of decline of complex networks by employing and analysing an illness model. Its intrinsic relation with the Fermi distribution is shown and a mapping to Fermi gas is established. The results of numerical simulations are obtained in two ways. We also compare the model with other models, including the dual relationship with the fitness model, and its difference from the Cayley tree model.
Understanding and Using the Fermi Science Tools
Asercion, Joseph; Fermi Science Support Center
2017-01-01
The Fermi Science Support Center (FSSC) provides information, documentation, and tools for the analysis of Fermi science data, including both the Large-Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). Source and binary versions of the Fermi Science Tools can be downloaded from the FSSC website, and are supported on multiple platforms. An overview document, the Cicerone, provides details of the Fermi mission, the science instruments and their response functions, the science data preparation and analysis process, and interpretation of the results. Analysis Threads and a reference manual available on the FSSC website provide the user with step-by-step instructions for many different types of data analysis: point source analysis - generating maps, spectra, and light curves, pulsar timing analysis, source identification, and the use of python for scripting customized analysis chains. We present an overview of the structure of the Fermi science tools and documentation, and how to acquire them. We also provide examples of standard analyses, including tips and tricks for improving Fermi science analysis.
An ancilla-based quantum simulation framework for non-unitary matrices
Daskin, Ammar; Kais, Sabre
2017-01-01
The success probability in an ancilla-based circuit generally decreases exponentially in the number of qubits consisted in the ancilla. Although the probability can be amplified through the amplitude amplification process, the input dependence of the amplitude amplification makes difficult to sequentially combine two or more ancilla-based circuits. A new version of the amplitude amplification known as the oblivious amplitude amplification runs independently of the input to the system register. This allows us to sequentially combine two or more ancilla-based circuits. However, this type of the amplification only works when the considered system is unitary or non-unitary but somehow close to a unitary. In this paper, we present a general framework to simulate non-unitary processes on ancilla-based quantum circuits in which the success probability is maximized by using the oblivious amplitude amplification. In particular, we show how to extend a non-unitary matrix to an almost unitary matrix. We then employ the extended matrix by using an ancilla-based circuit design along with the oblivious amplitude amplification. Measuring the distance of the produced matrix to the closest unitary matrix, a lower bound for the fidelity of the final state obtained from the oblivious amplitude amplification process is presented. Numerical simulations for random matrices of different sizes show that independent of the system size, the final amplified probabilities are generally around 0.75 and the fidelity of the final state is mostly high and around 0.95. Furthermore, we discuss the complexity analysis and show that combining two such ancilla-based circuits, a matrix product can be implemented. This may lead us to efficiently implement matrix functions represented as infinite matrix products on quantum computers.
Energy and contact of the one-dimensional Fermi polaron at zero and finite temperature.
Doggen, E V H; Kinnunen, J J
2013-07-12
We use the T-matrix approach for studying highly polarized homogeneous Fermi gases in one dimension with repulsive or attractive contact interactions. Using this approach, we compute ground state energies and values for the contact parameter that show excellent agreement with exact and other numerical methods at zero temperature, even in the strongly interacting regime. Furthermore, we derive an exact expression for the value of the contact parameter in one dimension at zero temperature. The model is then extended and used for studying the temperature dependence of ground state energies and the contact parameter.
Secure two-party quantum evaluation of unitaries against specious adversaries
Dupuis, Frédéric; Salvail, Louis
2010-01-01
We describe how any two-party quantum computation, specified by a unitary which simultaneously acts on the registers of both parties, can be privately implemented against a quantum version of classical semi-honest adversaries that we call specious. Our construction requires two ideal functionalities to garantee privacy: a private SWAP between registers held by the two parties and a classical private AND-box equivalent to oblivious transfer. If the unitary to be evaluated is in the Clifford group then only one call to SWAP is required for privacy. On the other hand, any unitary not in the Clifford requires one call to an AND-box per R-gate in the circuit. Since SWAP is itself in the Clifford group, this functionality is universal for the private evaluation of any unitary in that group. SWAP can be built from a classical bit commitment scheme or an AND-box but an AND-box cannot be constructed from SWAP. It follows that unitaries in the Clifford group are to some extent the easy ones. We also show that SWAP cann...
Matrix elements and duality for type 2 unitary representations of the Lie superalgebra gl(m|n)
Energy Technology Data Exchange (ETDEWEB)
Werry, Jason L.; Gould, Mark D.; Isaac, Phillip S. [School of Mathematics and Physics, The University of Queensland, St Lucia, QLD 4072 (Australia)
2015-12-15
The characteristic identity formalism discussed in our recent articles is further utilized to derive matrix elements of type 2 unitary irreducible gl(m|n) modules. In particular, we give matrix element formulae for all gl(m|n) generators, including the non-elementary generators, together with their phases on finite dimensional type 2 unitary irreducible representations which include the contravariant tensor representations and an additional class of essentially typical representations. Remarkably, we find that the type 2 unitary matrix element equations coincide with the type 1 unitary matrix element equations for non-vanishing matrix elements up to a phase.
A Fast Algorithm for Finding Point Sources in the Fermi Data Stream: FermiFAST
Ashathaman, Asha; Heyl, Jeremy S
2016-01-01
This paper presents a new and efficient algorithm for finding point sources in the photon event data stream from the Fermi Gamma-Ray Space Telescope. It can rapidly construct about most significant half of the Fermi Third Point Source catalogue (3FGL) with nearly 80% purity from the four years of data used to construct the catalogue. If a higher purity sample is desirable, one can achieve a sample that includes the most significant third of the Fermi 3FGL with only five percent of the sources unassociated with Fermi sources. Outside the galaxy plane, the contamination is essentially negligible. This software allows for rapid exploration of the Fermi data, simulation of the source detection to calculate the selection function of various sources and the errors in the obtained parameters of the sources detected.
Loh, Yen Lee; Trivedi, Nandini
2010-04-23
A system with unequal populations of up and down fermions may exhibit a Larkin-Ovchinnikov (LO) phase consisting of a periodic arrangement of domain walls where the order parameter changes sign and the excess polarization is localized. We find that the LO phase has a much larger range of stability in a lattice compared to the continuum; in a harmonic trap, the LO phase may involve 80% of the atoms in the trap, and can exist up to an entropy s approximately 0.5k(B) per fermion. We discuss detection of the LO phase (i) in real space by phase-contrast imaging of the periodic excess polarization; (ii) in k space by time-of-flight imaging of the single-particle and pair-momentum distributions; (iii) in energy space from the excess density of states within the gap arising from Andreev bound states in the domain walls.
Upgrading Fermi Without Traveling to Space
Kohler, Susanna
2016-02-01
The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope has received an upgrade that increased its sensitivity by a whopping 40% and nobody had to travel to space to make it happen! The difference instead stems from remarkable improvement to the software used to analyze Fermi-LATs data, and it has resulted in a new high-energy map of our sky.Animation (click to watch!) comparing the Pass 7 to the Pass 8 Fermi-LAT analysis, in a region in the constellation Carina. Pass 8 provides more accurate directions for incoming gamma rays, so more of them fall closer to their sources, creating taller spikes and a sharper image. [NASA/DOE/Fermi LAT Collaboration]Pass 8Fermi-LAT has been surveying the whole sky since August 2008. It detects gamma-ray photons by converting them into electron-positron pairs and tracking the paths of these charged particles. But differentiating this signal from the charged cosmic rays that also pass through the detector with a flux that can be 10,000 times larger! is a challenging process. Making this distinction and rebuilding the path of the original gamma ray relies on complex analysis software.Pass 8 is a complete reprocessing of all data collected by Fermi-LAT. The software has gone through many revisions before now, but this is the first revision that has taken into account all of the experience that the Fermi team has gained operating the LAT in its orbital environment.The improvements made in Pass 8 include better background rejection of misclassified charged particles, improvements to the point spread function and effective area of the detector, and an extension of the effective energy range from below 100 MeV to beyond a few hundred GeV. The changes made in Pass 8 have increased the sensitivity of Fermi-LAT by an astonishing 40%.Map of the High-Energy SkySky map of the sources in the 2FHL catalog, classified by their most likely association. Click for a better look! [Ackermann et al. 2016]The first result from the
A note on local unitary equivalence of isotropic-like states
Zhang, Ting-Gui; Hua, Bo-Bo; Li, Ming; Zhao, Ming-Jing; Yang, Hong
2015-12-01
We consider the local unitary equivalence of a class of quantum states in a bipartite case and a multipartite case. The necessary and sufficient condition is presented. As special cases, the local unitary equivalent classes of isotropic state and Werner state are provided. Then we study the local unitary similar equivalence of this class of quantum states and analyze the necessary and sufficient condition. Project supported by the National Natural Science Foundation of China (Grant Nos. 11401032, 61473325, 11501153, 11105226, 11275131, and 11401106), the Fundamental Research Funds for the Central Universities, China (Grant Nos. 15CX08011A and 24720122013), the Natural Science Foundation of Hainan Province, China (Grant Nos. 20151005 and 20151010), and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.
Accurate and robust unitary transformation of a high-dimensional quantum system
Anderson, B E; Riofrío, C A; Deutsch, I H; Jessen, P S
2014-01-01
Quantum control in large dimensional Hilbert spaces is essential for realizing the power of quantum information processing. For closed quantum systems the relevant input/output maps are unitary transformations, and the fundamental challenge becomes how to implement these with high fidelity in the presence of experimental imperfections and decoherence. For two-level systems (qubits) most aspects of unitary control are well understood, but for systems with Hilbert space dimension d>2 (qudits), many questions remain regarding the optimal design of control Hamiltonians and the feasibility of robust implementation. Here we show that arbitrary, randomly chosen unitary transformations can be efficiently designed and implemented in a large dimensional Hilbert space (d=16) associated with the electronic ground state of atomic 133Cs, achieving fidelities above 0.98 as measured by randomized benchmarking. Generalizing the concepts of inhomogeneous control and dynamical decoupling to d>2 systems, we further demonstrate t...
DOA estimation for monostatic MIMO radar based on unitary root-MUSIC
Wang, Wei; Wang, Xianpeng; Li, Xin; Song, Hongru
2013-11-01
Direction of arrival (DOA) estimation is an important issue for monostatic MIMO radar. A DOA estimation method for monostatic MIMO radar based on unitary root-MUSIC is presented in this article. In the presented method, a reduced-dimension matrix is first utilised to transform the high dimension of received signal data into low dimension one. Then, a low-dimension real-value covariance matrix is obtained by forward-backward (FB) averaging and unitary transformation. The DOA of targets can be achieved by unitary root-MUSIC. Due to the FB averaging of received signal data and the eigendecomposition of the real-valued matrix covariance, the proposed method owns better angle estimation performance and lower computational complexity. The simulation results of the proposed method are presented and the performances are investigated and discussed.
NMR Hyperpolarization Techniques of Gases.
Barskiy, Danila A; Coffey, Aaron M; Nikolaou, Panayiotis; Mikhaylov, Dmitry M; Goodson, Boyd M; Branca, Rosa T; Lu, George J; Shapiro, Mikhail G; Telkki, Ville-Veikko; Zhivonitko, Vladimir V; Koptyug, Igor V; Salnikov, Oleg G; Kovtunov, Kirill V; Bukhtiyarov, Valerii I; Rosen, Matthew S; Barlow, Michael J; Safavi, Shahideh; Hall, Ian P; Schröder, Leif; Chekmenev, Eduard Y
2017-01-18
Nuclear spin polarization can be significantly increased through the process of hyperpolarization, leading to an increase in the sensitivity of nuclear magnetic resonance (NMR) experiments by 4-8 orders of magnitude. Hyperpolarized gases, unlike liquids and solids, can often be readily separated and purified from the compounds used to mediate the hyperpolarization processes. These pure hyperpolarized gases enabled many novel MRI applications including the visualization of void spaces, imaging of lung function, and remote detection. Additionally, hyperpolarized gases can be dissolved in liquids and can be used as sensitive molecular probes and reporters. This Minireview covers the fundamentals of the preparation of hyperpolarized gases and focuses on selected applications of interest to biomedicine and materials science. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Bosse, J; Pathak, K N; Singh, G S
2011-10-01
The fluctuation-dissipation theorem together with the exact density response spectrum for ideal quantum gases has been utilized to yield a new expression for the static structure factor, which we use to derive exact analytical expressions for the temperature-dependent pair distribution function g(r) of the ideal gases. The plots of bosonic and fermionic g(r) display "Bose pile" and "Fermi hole" typically akin to bunching and antibunching as observed experimentally for ultracold atomic gases. The behavior of spin-scaled pair correlation for fermions is almost featureless, but bosons show a rich structure including long-range correlations near T(c). The coherent state at T=0 shows no correlation at all, just like single-mode lasers. The depicted decreasing trend in correlation with decrease in temperature for T
Shock instability in dissipative gases
Radulescu, Matei I.; Sirmas, Nick
2011-01-01
Previous experiments have revealed that shock waves in thermally relaxing gases, such as ionizing, dissociating and vibrationally excited gases, can become unstable. To date, the mechanism controlling this instability has not been resolved. Previous accounts of the D'yakov-Kontorovich instability, and Bethe-Zel'dovich-Thompson behaviour could not predict the experimentally observed instability. To address the mechanism controlling the instability, we study the propagation of shock waves in a ...
Universal spin transport in a strongly interacting Fermi gas.
Sommer, Ariel; Ku, Mark; Roati, Giacomo; Zwierlein, Martin W
2011-04-14
Transport of fermions, particles with half-integer spin, is central to many fields of physics. Electron transport runs modern technology, defining states of matter such as superconductors and insulators, and electron spin is being explored as a new carrier of information. Neutrino transport energizes supernova explosions following the collapse of a dying star, and hydrodynamic transport of the quark-gluon plasma governed the expansion of the early Universe. However, our understanding of non-equilibrium dynamics in such strongly interacting fermionic matter is still limited. Ultracold gases of fermionic atoms realize a pristine model for such systems and can be studied in real time with the precision of atomic physics. Even above the superfluid transition, such gases flow as an almost perfect fluid with very low viscosity when interactions are tuned to a scattering resonance. In this hydrodynamic regime, collective density excitations are weakly damped. Here we experimentally investigate spin excitations in a Fermi gas of (6)Li atoms, finding that, in contrast, they are maximally damped. A spin current is induced by spatially separating two spin components and observing their evolution in an external trapping potential. We demonstrate that interactions can be strong enough to reverse spin currents, with components of opposite spin reflecting off each other. Near equilibrium, we obtain the spin drag coefficient, the spin diffusivity and the spin susceptibility as a function of temperature on resonance and show that they obey universal laws at high temperatures. In the degenerate regime, the spin diffusivity approaches a value set by [planck]/m, the quantum limit of diffusion, where [planck]/m is Planck's constant divided by 2π and m the atomic mass. For repulsive interactions, our measurements seem to exclude a metastable ferromagnetic state.
Beyond the 2nd Fermi Pulsar Catalog
Hou, Xian; Reposeur, Thierry; Rousseau, Romain
2013-01-01
Over thirteen times more gamma-ray pulsars have now been studied with the Large Area Telescope on NASA's Fermi satellite than the ten seen with the Compton Gamma-Ray Observatory in the nineteen-nineties. The large sample is diverse, allowing better understanding both of the pulsars themselves and of their roles in various cosmic processes. Here we explore the prospects for even more gamma-ray pulsars as Fermi enters the 2nd half of its nominal ten-year mission. New pulsars will naturally tend to be fainter than the first ones discovered. Some of them will have unusual characteristics compared to the current population, which may help discriminate between models. We illustrate a vision of the future with a sample of six pulsars discovered after the 2nd Fermi Pulsar Catalog was written.
Fermi's Paradox - The Last Challenge for Copernicanism?
Cirkovic, Milan M
2009-01-01
We review Fermi's paradox (or the "Great Silence" problem), not only arguably the oldest and crucial problem for the Search for ExtraTerrestrial Intelligence (SETI), but also a conundrum of profound scientific, philosophical and cultural importance. By a simple analysis of observation selection effects, the correct resolution of Fermi's paradox is certain to tell us something about the future of humanity. Already a more than three quarters of a century old puzzle - and a quarter of century since the last major review paper in the field by G. David Brin - Fermi's paradox has generated many ingenious discussions and hypotheses. We analyze the often tacit methodological assumptions built into various answers to this puzzle and attempt a new classification of the numerous solutions proposed in an already huge literature on the subject. Finally, we consider the ramifications of various classes of hypotheses for the practical SETI projects. Somewhat paradoxically, it seems that the class of (neo)catastrophic hypoth...
Maier, T A; Staar, P; Mishra, V; Chatterjee, U; Campuzano, J C; Scalapino, D J
2016-06-17
In the traditional Bardeen-Cooper-Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and -k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. Here we report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. In contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin-fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability.
Fujii, Kazuyuki
2008-01-01
In this paper we treat the time evolution of unitary elements in the N level system and consider the reduced dynamics from the unitary group U(N) to flag manifolds of the second type (in our terminology). Then we derive a set of differential equations of matrix Riccati types interacting with one another and present an important problem on a nonlinear superposition formula that the Riccati equation satisfies. Our result is a natural generalization of the paper {\\bf Chaturvedi et al} (arXiv : 0706.0964 [quant-ph]).
Study of optical techniques for the Ames unitary wind tunnel, part 7
Lee, George
1993-01-01
A summary of optical techniques for the Ames Unitary Plan wind tunnels are discussed. Six optical techniques were studied: Schlieren, light sheet and laser vapor screen, angle of attack, model deformation, infrared imagery, and digital image processing. The study includes surveys and reviews of wind tunnel optical techniques, some conceptual designs, and recommendations for use of optical methods in the Ames Unitary Plan wind tunnels. Particular emphasis was placed on searching for systems developed for wind tunnel use and on commercial systems which could be readily adapted for wind tunnels. This final report is to summarize the major results and recommendations.
Classical 1D maps, quantum graphs and ensembles of unitary matrices
Energy Technology Data Exchange (ETDEWEB)
Pakonski, Prot [Uniwersytet Jagiellonski, Instytut Fizyki im. M. Smoluchowskiego, Cracow (Poland)]. E-mail: pakonski@if.uj.edu.pl; Zyczkowski, Karol; Kus, Marek [Centrum Fizyki Teoretycznej PAN, Warsaw (Poland)]. E-mails: karol@cft.edu.pl; marek@cft.edu.pl
2001-10-26
We study a certain class of classical one-dimensional piecewise linear maps. For these systems we introduce an infinite family of Markov partitions in equal cells. The symbolic dynamics generated by these systems is described by bi-stochastic (doubly stochastic) matrices. We analyse the structure of graphs generated from the corresponding symbolic dynamics. We demonstrate that the spectra of quantized graphs corresponding to the regular classical systems have locally Poissonian statistics, while quantized graphs derived from classically chaotic systems display statistical properties characteristic of the circular unitary ensemble, even though the corresponding unitary matrices are sparse. (author)
Elementary Proof for Asymptotics of Large Haar-Distributed Unitary Matrices
Mastrodonato, Christian; Tumulka, Roderich
2007-01-01
We provide an elementary proof for a theorem due to Petz and R\\'effy which states that for a random $n\\times n$ unitary matrix with distribution given by the Haar measure on the unitary group U(n), the upper left (or any other) $k\\times k$ submatrix converges in distribution, after multiplying by a normalization factor $\\sqrt{n}$ and as $n\\to\\infty$, to a matrix of independent complex Gaussian random variables with mean 0 and variance 1.
Unitary representations of the Poincaré group and relativistic wave equations
Ohnuki, Yoshio
1976-01-01
This book is devoted to an extensive and systematic study on unitary representations of the Poincaré group. The Poincaré group plays an important role in understanding the relativistic picture of particles in quantum mechanics. Complete knowledge of every free particle states and their behaviour can be obtained once all the unitary irreducible representations of the Poincaré group are found. It is a surprising fact that a simple framework such as the Poincaré group, when unified with quantum theory, fixes our possible picture of particles severely and without exception. In this connection, the
Unitary evolution for anisotropic quantum cosmologies: models with variable spatial curvature
Pandey, Sachin
2016-01-01
Contrary to the general belief, there has recently been quite a few examples of unitary evolution of quantum cosmological models. The present work gives more examples, namely Bianchi type VI and type II. These examples are important as they involve varying spatial curvature unlike the most talked about homogeneous but anisotropic cosmological models like Bianchi I, V and IX. We exhibit either explicit example of the unitary solutions of the Wheeler-DeWitt equation, or at least show that a self-adjoint extension is possible.
Unitary evolution for anisotropic quantum cosmologies: models with variable spatial curvature
Pandey, Sachin; Banerjee, Narayan
2016-11-01
Contrary to the general belief, there has recently been quite a few examples of unitary evolution of quantum cosmological models. The present work gives more examples, namely Bianchi type VI and type II. These examples are important as they involve varying spatial curvature unlike the most talked about homogeneous but anisotropic cosmological models like Bianchi I, V and IX. We exhibit either an explicit example of the unitary solutions of the Wheeler-DeWitt equation, or at least show that a self-adjoint extension is possible.
Energy-pressure relation for low-dimensional gases
Mancarella, Francesco; Mussardo, Giuseppe; Trombettoni, Andrea
2014-10-01
A particularly simple relation of proportionality between internal energy and pressure holds for scale-invariant thermodynamic systems (with Hamiltonians homogeneous functions of the coordinates), including classical and quantum - Bose and Fermi - ideal gases. One can quantify the deviation from such a relation by introducing the internal energy shift as the difference between the internal energy of the system and the corresponding value for scale-invariant (including ideal) gases. After discussing some general thermodynamic properties associated with the scale-invariance, we provide criteria for which the internal energy shift density of an imperfect (classical or quantum) gas is a bounded function of temperature. We then study the internal energy shift and deviations from the energy-pressure proportionality in low-dimensional models of gases interpolating between the ideal Bose and the ideal Fermi gases, focusing on the Lieb-Liniger model in 1d and on the anyonic gas in 2d. In 1d the internal energy shift is determined from the thermodynamic Bethe ansatz integral equations and an explicit relation for it is given at high temperature. Our results show that the internal energy shift is positive, it vanishes in the two limits of zero and infinite coupling (respectively the ideal Bose and the Tonks-Girardeau gas) and it has a maximum at a finite, temperature-depending, value of the coupling. Remarkably, at fixed coupling the energy shift density saturates to a finite value for infinite temperature. In 2d we consider systems of Abelian anyons and non-Abelian Chern-Simons particles: as it can be seen also directly from a study of the virial coefficients, in the usually considered hard-core limit the internal energy shift vanishes and the energy is just proportional to the pressure, with the proportionality constant being simply the area of the system. Soft-core boundary conditions at coincident points for the two-body wavefunction introduce a length scale, and induce a
Pseudogap-generated a coexistence of Fermi arcs and Fermi pockets in cuprate superconductors
Zhao, Huaisong; Gao, Deheng; Feng, Shiping
2017-03-01
One of the most intriguing puzzle is why there is a coexistence of Fermi arcs and Fermi pockets in the pseudogap phase of cuprate superconductors? This puzzle is calling for an explanation. Based on the t - J model in the fermion-spin representation, the coexistence of the Fermi arcs and Fermi pockets in cuprate superconductors is studied by taking into account the pseudogap effect. It is shown that the pseudogap induces an energy band splitting, and then the poles of the electron Green's function at zero energy form two contours in momentum space, however, the electron spectral weight on these two contours around the antinodal region is gapped out by the pseudogap, leaving behind the low-energy electron spectral weight only located at the disconnected segments around the nodal region. In particular, the tips of these disconnected segments converge on the hot spots to form the closed Fermi pockets, generating a coexistence of the Fermi arcs and Fermi pockets. Moreover, the single-particle coherent weight is directly related to the pseudogap, and grows linearly with doping. The calculated result of the overall dispersion of the electron excitations is in qualitative agreement with the experimental data. The theory also predicts that the pseudogap-induced peak-dip-hump structure in the electron spectrum is absent from the hot-spot directions.
Supernova Remnants with Fermi Large Area Telescope
Directory of Open Access Journals (Sweden)
Caragiulo M.
2017-01-01
Full Text Available The Large Area Telescope (LAT, on-board the Fermi satellite, proved to be, after 8 years of data taking, an excellent instrument to detect and observe Supernova Remnants (SNRs in a range of energies running from few hundred MeV up to few hundred GeV. It provides essential information on physical processes that occur at the source, involving both accelerated leptons and hadrons, in order to understand the mechanisms responsible for the primary Cosmic Ray (CR acceleration. We show the latest results in the observation of Galactic SNRs by Fermi-LAT.
Clustering in the nuclear Fermi liquid
Ebran, J -P; Niksic, T; Vretenar, D
2012-01-01
We analyze the emergence of various structures in nucleonic matter, such as crystal, clusters, liquid drops and haloes. The formation of clusters indicates that nuclei behave like a Fermi liquid close to the liquid to solid transition. The relevant parameter is the ratio of the dispersion of the single-nucleon wave functions in the nucleus to the inter-nucleon distance. We also discuss the relationship between cluster states in nuclei and the pasta phase in the crust of neutron stars, as a transitional state between a Fermi liquid and a crystal. Haloes and clusters exhibit opposite features with respect to nucleonic localization.
DEFF Research Database (Denmark)
Antipin, Oleg; Sannino, Francesco; Tuominen, Kimmo
2013-01-01
The discovery of a light Higgs boson at LHC may be suggesting that we need to revise our model building paradigms to understand the origin of the weak scale. We explore the possibility that the Fermi scale is not fundamental but rather a derived one, i.e. a low energy mirage. We show that this sc......The discovery of a light Higgs boson at LHC may be suggesting that we need to revise our model building paradigms to understand the origin of the weak scale. We explore the possibility that the Fermi scale is not fundamental but rather a derived one, i.e. a low energy mirage. We show...
MASTER: OT detection during Fermi trigger inspection
Popova, E.; Lipunov, V.; Buckley, D.; Gorbovskoy, E.; Tiurina, N.; Balanutsa, P.; Kuznetsov, A.; Kornilov, V.; Chazov, V.; Vlasenko, D.; Vladimirov, V.; Gress, O.; Ivanov, K.; Potter, S.; Gabovich, A.
2016-11-01
During inspection of Fermi trigger 501261070 ( (Ra,Dec)=47.190,-47.210; GRB_ERROR_radius=3.27deg, GRB_TIME=2016/11/19 15:11:06.40UT http://gcn.gsfc.nasa.gov/other/501261070.fermi ) MASTER-SAAO auto-detection system ( Lipunov et al., "MASTER Global Robotic Net", Advances in Astronomy, 2010, 30L ) discovered OT source at (RA, Dec) = 03h 22m 52.70s -48d 29m 10.9s on 2016-11-19 21:17:17.878UT with unfiltered m_OT=17.8 (mlim=19.7).
Scattering resonances in a degenerate Fermi gas
DEFF Research Database (Denmark)
Challis, Katharine; Nygaard, Nicolai; Mølmer, Klaus
2009-01-01
We consider elastic single-particle scattering from a one-dimensional trapped two-component superfluid Fermi gas when the incoming projectile particle is identical to one of the confined species. Our theoretical treatment is based on the Hartree-Fock ground state of the trapped gas and a configur......We consider elastic single-particle scattering from a one-dimensional trapped two-component superfluid Fermi gas when the incoming projectile particle is identical to one of the confined species. Our theoretical treatment is based on the Hartree-Fock ground state of the trapped gas...
Deep Inelastic Scattering on Ultracold Gases
Hofmann, Johannes; Zwerger, Wilhelm
2017-01-01
We discuss Bragg scattering on both Bose and Fermi gases with strong short-range interactions in the deep inelastic regime of large wave vector transfer q , where the dynamic structure factor is dominated by a resonance near the free-particle energy ℏω =ɛq=ℏ2q2/2 m . Using a systematic short-distance expansion, the structure factor at high momentum is shown to exhibit a nontrivial dependence on frequency characterized by two separate scaling regimes. First, for frequencies that differ from the single-particle energy by terms of order O (q ) (i.e., small deviations compared to the single-particle energy), the dynamic structure factor is described by the impulse approximation of Hohenberg and Platzman. Second, deviations of order O (q2) (i.e., of the same order or larger than the single-particle energy) are described by the operator product expansion, with a universal crossover connecting both regimes. The scaling is consistent with the leading asymptotics for a number of sum rules in the large momentum limit. Furthermore, we derive an exact expression for the shift and width of the single-particle peak at large momentum due to interactions, thus extending a result by Beliaev [J. Exp. Theor. Phys. 7, 299 (1958)] for the low-density Bose gas to arbitrary values of the scattering length a . The shift exhibits a maximum around q a ≃1 , which is connected with a maximum in the static structure factor due to strong short-range correlations. For Bose gases with moderate interaction strengths, the theoretically predicted shift is consistent with the value observed by Papp et al. [Phys. Rev. Lett. 101, 135301 (2008), 10.1103/PhysRevLett.101.135301]. Finally, we develop a diagrammatic theory for the dynamic structure factor which accounts for the correlations beyond Bogoliubov theory. It covers the full range of momenta and frequencies and provides an explicit example for the emergence of asymptotic scaling at large momentum.
Thermodynamics and statistical mechanics. [thermodynamic properties of gases
1976-01-01
The basic thermodynamic properties of gases are reviewed and the relations between them are derived from the first and second laws. The elements of statistical mechanics are then formulated and the partition function is derived. The classical form of the partition function is used to obtain the Maxwell-Boltzmann distribution of kinetic energies in the gas phase and the equipartition of energy theorem is given in its most general form. The thermodynamic properties are all derived as functions of the partition function. Quantum statistics are reviewed briefly and the differences between the Boltzmann distribution function for classical particles and the Fermi-Dirac and Bose-Einstein distributions for quantum particles are discussed.
Spin Relaxation in Hyperpolarized He-3 Fermi Liquids
Stanton, Liam; Bedell, Kevin
2004-03-01
In the past few years, attention has been drawn towards the hyperpolarized gases of Xenon-129 and Helium-3 isotopes. Medical research has explored the possibilities of using these isotopes for magnetic resonance imaging (MRI) of the lungs in both human and animal test subjects. Because the atoms of hyperpolarized gas are forced into a specific spin state, the MRI signal is enhanced. While the spin relaxation times of Helium-3 can be calculated in the high and low temperature limits, there exists no exact analytic solution for intermediate temperatures. The intention of this research was to numerically connect these limits with an accurate approximation. To do this, various analytic and numerical methods were used to reduce the spin relaxation time to a function of temperature, chemical potential, and particle number. Additional numerical methods were then used to calculate the chemical potential of Helium-3. The data show that a minimum occurs in the spin relaxation time at the order of the Fermi temperature, after which the classical limit is rapidly approached. These computational results seem to coincide with those expected.
40 CFR 1065.750 - Analytical gases.
2010-07-01
... 40 Protection of Environment 32 2010-07-01 2010-07-01 false Analytical gases. 1065.750 Section... ENGINE-TESTING PROCEDURES Engine Fluids, Test Fuels, Analytical Gases and Other Calibration Standards § 1065.750 Analytical gases. Analytical gases must meet the accuracy and purity specifications of...
Observation of a pairing pseudogap in a two-dimensional Fermi gas.
Feld, Michael; Fröhlich, Bernd; Vogt, Enrico; Koschorreck, Marco; Köhl, Michael
2011-11-30
Pairing of fermions is ubiquitous in nature, underlying many phenomena. Examples include superconductivity, superfluidity of (3)He, the anomalous rotation of neutron stars, and the crossover between Bose-Einstein condensation of dimers and the BCS (Bardeen, Cooper and Schrieffer) regime in strongly interacting Fermi gases. When confined to two dimensions, interacting many-body systems show even more subtle effects, many of which are not understood at a fundamental level. Most striking is the (as yet unexplained) phenomenon of high-temperature superconductivity in copper oxides, which is intimately related to the two-dimensional geometry of the crystal structure. In particular, it is not understood how the many-body pairing is established at high temperature, and whether it precedes superconductivity. Here we report the observation of a many-body pairing gap above the superfluid transition temperature in a harmonically trapped, two-dimensional atomic Fermi gas in the regime of strong coupling. Our measurements of the spectral function of the gas are performed using momentum-resolved photoemission spectroscopy, analogous to angle-resolved photoemission spectroscopy in the solid state. Our observations mark a significant step in the emulation of layered two-dimensional strongly correlated superconductors using ultracold atomic gases.
The Physical and Dynamical Properties of Gas that Molds the Fermi Bubbles
Jenkins, Edward
2012-10-01
Two sharply defined lobes of gamma-ray emission emerging from the center of our Galaxy, called the Fermi Bubbles, have been discovered in the Galactic halo. Their emissivity appears to be uniform and extends up to 8 kpc on either side of the plane. Accompanying the Fermi Bubbles are excess emissions seen in X-rays and microwaves. It is generally believed that cosmic ray particles emitted from the central portion of the Galactic disk {or perhaps the nucleus itself} are responsible for these emissions. These particles must have been advected into the halo by a wind or shock. Our goal is to gain a better understanding of the nature of this gaseous transport by viewing the UV spectra of bright, extragalactic sources behind one of the Fermi Bubbles and its surrounding regions. We plan to obtain COS spectra of 5 such objects, with the goal of measuring absorption features from Si III, Si IV, C IV and N V. We expect that our mapping of column densities and kinematics of the gases will help us to distinguish a shock from a wind. Moreover, if a shock is present, we should be able to evaluate the product of its age and the density of the gas by comparing the column densities of different species.
A two-dimensional Fermi gas in the BEC-BCS crossover
Energy Technology Data Exchange (ETDEWEB)
Ries, Martin Gerhard
2016-01-21
This thesis reports on the preparation of a 2D Fermi gas in the BEC-BCS crossover and the observation of the BKT transition into a quasi long-range ordered superfluid phase. The pair momentum distribution of the gas is probed by means of a matter-wave focusing technique which relies on time-of-flight evolution in a weak harmonic potential. This distribution holds the coherence properties of the gas. The quasi long-range ordered phase manifests itself as a sharp low-momentum peak. The temperature where it forms is identified as the transition temperature. By tuning the temperature and the interaction strength, the phase diagram of the 2D Fermi gas in the BEC-BCS crossover is mapped out. The phase coherence is investigated in a self-interference experiment. Furthermore, algebraic decay of correlations is observed in the trap average of the first order correlation function, which is obtained from the Fourier transform of the pair momentum distribution. This is in qualitative agreement with predictions of homogeneous theory for the superfluid phase in a 2D gas. The presented results provide a foundation for future experimental and theoretical studies of strongly correlated 2D Fermi gases. They might thus help to elucidate complex systems such as the electron gas in high-T{sub c} superconductors.
Indian Academy of Sciences (India)
Bihong Lin; Yingru Zhao; Jincan Chen
2008-05-01
An irreversible model of an Ericsson cryogenic refrigeration cycle working with an ideal Fermi gas is established, which is composed of two isothermal and two isobaric processes. The influence of both the quantum degeneracy and the finite-rate heat transfer between the working fluid and the heat reservoirs on the performance of the cycle is investigated, based on the theory of statistical mechanics and thermodynamic properties of an ideal Fermi gas. The inherent regeneration losses of the cycle are analyzed. Expressions for several important performance parameters such as the coefficient of performance, cooling rate and power input are derived. By using numerical solutions, the cooling rate of the cycle is optimized for a given power input. The maximum cooling rate and the corresponding parameters are calculated numerically. The optimal regions of the coefficient of performance and power input are determined. Especially, the optimal performance of the cycle in the strong and weak gas degeneracy cases and the high temperature limit is discussed in detail. The analytic expressions of some optimized parameters are derived. Some optimum criteria are given. The distinctions and connections between the Ericsson refrigeration cycles working with the Fermi and classical gases are revealed.
Novel differential unitary space-time modulation schemes for fast fading channels
Institute of Scientific and Technical Information of China (English)
Tian Jifeng; Jiang Haining; Song Wentao; Luo Hanwen
2006-01-01
Differential unitary space-time modulation (DUSTM), which obtains full transmit diversity in slowly flat-fading channels without channel state information, has generated significant interests recently. To combat frequency-selective fading, DUSTM has been applied to each subcarrier of an OFDM system and DUSTM-OFDM system was proposed. Both DUSTM and DUSTM-OFDM, however, are designed for slowly fading channels and suffer performance deterioration in fast fading channels. In this paper, two novel differential unitary space-time modulation schemes are proposed for fast fading channels. For fast flat-fading channels, a sub-matrix interleaved DUSTM (SMI-DUSTM) scheme is proposed, in which matrix-segmentation and sub-matrix based interleaving are introduced into DUSTM system. For fast frequency-selective fading channels, a differential unitary space-frequency modulation (DUSFM) scheme is proposed, in which existing unitary space-time codes are employed across transmit antennas and OFDM subcarriers simultaneously and differential modulation is performed between two adjacent OFDM blocks. Compared with DUSTM and DUSTM-OFDM schemes, SMI-DUSTM and DUSFM-OFDM are more robust to fast channel fading with low decoding complexity, which is demonstrated by performance analysis and simulation results.
J(l)-unitary factorization and the Schur algorithm for Nevanlinna functions in an indefinite setting
Alpay, D.; Dijksma, A.; Langer, H.
2006-01-01
We introduce a Schur transformation for generalized Nevanlinna functions and show that it can be used in obtaining the unique minimal factorization of a class of rational J(l)-unitary 2 x 2 matrix functions into elementary factors from the same class. (c) 2006 Elsevier Inc. All rights reserved.
Campoamor-Stursberg, R.; Rausch de Traubenberg, M.
2017-04-01
The representation theory of three dimensional real and complex Lie groups is reviewed from the perspective of harmonic functions defined over certain appropriate manifolds. An explicit construction of all unitary representations is given. The realisations obtained are shown to be related with each other by either natural operations as real forms or Inönü-Wigner contractions.
The flexible focus: whether spatial attention is unitary or divided depends on observer goals.
Jefferies, Lisa N; Enns, James T; Di Lollo, Vincent
2014-04-01
The distribution of visual attention has been the topic of much investigation, and various theories have posited that attention is allocated either as a single unitary focus or as multiple independent foci. In the present experiment, we demonstrate that attention can be flexibly deployed as either a unitary or a divided focus in the same experimental task, depending on the observer's goals. To assess the distribution of attention, we used a dual-stream Attentional Blink (AB) paradigm and 2 target pairs. One component of the AB, Lag-1 sparing, occurs only if the second target pair appears within the focus of attention. By varying whether the first-target-pair could be expected in a predictable location (always in-stream) or not (unpredictably in-stream or between-streams), observers were encouraged to deploy a divided or a unitary focus, respectively. When the second-target-pair appeared between the streams, Lag-1 sparing occurred for the Unpredictable group (consistent with a unitary focus) but not for the Predictable group (consistent with a divided focus). Thus, diametrically different outcomes occurred for physically identical displays, depending on the expectations of the observer about where spatial attention would be required.
On Parseval Wavelet Frames with Two or Three Generators via the Unitary Extension Principle
DEFF Research Database (Denmark)
Christensen, Ole; Kim, Hong Oh; Kim, Rae Young
2014-01-01
The unitary extension principle (UEP) by A. Ron and Z. Shen yields a sufficient condition for the construction of Parseval wavelet frames with multiple generators. In this paper we characterize the UEP-type wavelet systems that can be extended to a Parseval wavelet frame by adding just one UEP-ty...
Lorentz Spin-Foam with Non Unitary Representations by use of Holomorphic Peter-Weyl Theorem
Perlov, Leonid
2013-01-01
We use the non-unitary spinor representations of SL(2,C) and the recently proved Holomorphic Peter-Weyl theorem to define the Hilbert space based on the holomorphic spin-networks, the non-unitary spin-foam, solve the simplicity constraints and calculate the vertex amplitude. The diagonal simplicity constraint provides two solutions. The first solution: Immirzi $\\gamma = i$ with the irreducible representations $(j_1, j_2)$ projected to $(0, j)$ and the second solution: Immirzi $\\gamma = -i$ and the irreducible non-unitary representations projected to $(j, 0)$. The off-diagonal constraint selects only the first of these two solutions. The solution is interesting in two aspects: a) it turns to be a topological BF model. b) Immirzi parameter $\\gamma = i$ corresponds to Ashtekar's self-dual connection of the complexified algebra $sl(2,C)\\otimes C$. The transition amplitude is finite and very similar to BF Euclidean model. We discuss the inner product Lorentz invariance and the viability of the non-unitary represen...
Gaussian elimination in split unitary groups with an application to public-key cryptography
Directory of Open Access Journals (Sweden)
Ayan Mahalanobis
2017-07-01
Full Text Available Gaussian elimination is used in special linear groups to solve the word problem. In this paper, we extend Gaussian elimination to split unitary groups. These algorithms have an application in building a public-key cryptosystem, we demonstrate that.
Factorization and uniton numbers for harmonic maps into the unitary group U(N)
Institute of Scientific and Technical Information of China (English)
东瑜昕; 沈一兵
1996-01-01
The factorization of harmonic maps from a simply-connected domain to the unitary group is studied, showing that the theory of isotropic harmonic maps is equivalent to that of 2-unitons. Furthermore, a positive answer is given to the Uhlenbeck’s conjecture on the upper bound of minimal uniton numbers.
Entanglement capacity of two-qubit unitary operator for rank two mixed states
Institute of Scientific and Technical Information of China (English)
DI; YaoMin
2007-01-01
The entanglement capacity of two-qubit unitary operator acting on rank two mixed states in concurrence is discussed. The condition of perfect entangler is the same as that acting on pure states and the entanglement capacity is the mixing parameter v1. For non-perfect entangler, the upper and lower bound of the entanglement capacity are given.……
Secure Two-Party Quantum Evaluation of Unitaries against Specious Adversaries
DEFF Research Database (Denmark)
Dupuis, Frédéric; Nielsen, Jesper Buus; Salvail, Louis
2010-01-01
We describe how any two-party quantum computation, specified by a unitary which simultaneously acts on the registers of both parties, can be privately implemented against a quantum version of classical semi-honest adversaries that we call specious. Our construction requires two ideal functionalit...
Entanglement capacity of two-qubit unitary operator for rank two mixed states
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
@@ The entanglement capacity of two-qubit unitary operator acting on rank two mixed states in concurrence is discussed. The condition of perfect entangler is the same as that acting on pure states and the entanglement capacity is the mixing parameter v1. For non-perfect entangler, the upper and lower bound of the entanglement capacity are given.
Measuring the Leptonic CP Phase in Neutrino Oscillations with Non-Unitary Mixing
Ge, Shao-Feng; Tortola, M; Valle, J W F
2016-01-01
Non-unitary neutrino mixing implies an extra CP violating phase that can fake the leptonic Dirac CP phase $\\delta_{CP}$ of the simplest three-neutrino mixing benchmark scheme. This would hinder the possibility of probing for CP violation in accelerator-type experiments. We take T2K and T2HK as examples to demonstrate the degeneracy between the "standard" (or "unitary") and "non-unitary" CP phases. We find, under the assumption of non-unitary mixing, that their CP sensitivities severely deteriorate. Fortunately, the TNT2K proposal of supplementing T2(H)K with a $\\mu$DAR source for better measurement of $\\delta_{CP}$ can partially break the CP degeneracy by probing both $\\cos \\delta_{CP}$ and $\\sin \\delta_{CP}$ dependences in the wide spectrum of the $\\mu$DAR flux. We also show that the further addition of a near detector to the $\\mu$DAR setup can eliminate the degeneracy completely.
Fermi and the Theory of Weak Interactions
Rajasekaran, G
2014-01-01
The history of weak interactions starting with Fermi's creation of the beta decay theory and culminating in its modern avatar in the form of the electroweak gauge theory is described. Discoveries of parity violation, matter-antimatter asymmetry, W and Z bosons and neutrino mass are highlighted.
Fermi surface effects in terbium alloys
Energy Technology Data Exchange (ETDEWEB)
Burgardt, P.
1976-10-01
Work is reported which was conducted to test of the relation of the generalized susceptibility (and therefore, the ordering properties) for Tb to the Fermi energy of Tb. In order to properly analyze the data a simple theory was developed to account for the effects on band structure which accompany alloying and attendant lattice size changes. Using this simple theory, the alloys of Tb with Mg are understood as a combination of Fermi energy lowering and of lattice contraction. The tendency of Th to promote the ferromagnetic structure in Th is understood as a combination of the Fermi energy being raised and of the lattice being expanded. The theory was also useful in explaining the interesting behavior of the Tb with Yb alloys which upon preliminary analysis did not seem to follow the theoretical predictions. After consideration of the volume effect, indeed the Tb with Yb alloys showed promotion of the helical structure as predicted. The complicated behavior of the Tb with Yb alloys is a case where the volume and valence effects compete. Results show that the magnetic ordering properties of the rare earths are intimately related to the Fermi surface geometry through the generalized susceptibility.
Fermi detected blazars seen by INTEGRAL
Beckmann, V; Soldi, S
2009-01-01
Multiwavelength observations are essential to constrain physical parameters of the blazars observed by Fermi/LAT. Among the 187 AGN significantly detected in public INTEGRAL data above 20 keV by the imager IBIS/ISGRI, 20 blazars were detected. 15 of these sources allowed significant spectral extraction. They show hard X-ray spectra with an average photon index of 2.1+-0.1 and a hard X-ray luminosity of L(20-100 keV) = 1.3e46 erg/s. 15 of the INTEGRAL blazars are also visible in the first 16 months of the Fermi/LAT data, thus allowing to constrain the inverse Compton branch in these cases. Among others, we analyse the LAT data of four blazars which were not included in the Fermi LAT Bright AGN Sample based on the first 3 months of the mission: QSO B0836+710, H 1426+428, RX J1924.8-2914, and PKS 2149-306. Especially for blazars during bright outbursts, as already observed simultaneously by INTEGRAL and Fermi (e.g. 3C 454.3 and Mrk 421), INTEGRAL provides unique spectral coverage up to several hundred keV. We pr...
Switchable Fermi surface sheets in greigite
Zhang, B.; de Wijs, G. A.; de Groot, R. A.
2012-01-01
Greigite (Fe3S4) and magnetite (Fe3O4) are isostructural and isoelectronic ferrimagnets with quite distinct properties. Electronic structure calculations reveal greigite is a normalmetal in contrast to half-metallic magnetite. Greigite shows a complex Fermi surface with a unique influence of
FERMI LARGE AREA TELESCOPE SECOND SOURCE CATALOG
Energy Technology Data Exchange (ETDEWEB)
Nolan, P. L.; Ajello, M.; Allafort, A.; Bechtol, K.; Berenji, B.; Blandford, R. D.; Bloom, E. D. [W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States); Abdo, A. A. [Center for Earth Observing and Space Research, College of Science, George Mason University, Fairfax, VA 22030 (United States); Ackermann, M. [Deutsches Elektronen Synchrotron DESY, D-15738 Zeuthen (Germany); Antolini, E.; Bonamente, E. [Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia (Italy); Atwood, W. B.; Belfiore, A. [Santa Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064 (United States); Axelsson, M. [Department of Astronomy, Stockholm University, SE-106 91 Stockholm (Sweden); Baldini, L.; Bellazzini, R. [Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy); Ballet, J. [Laboratoire AIM, CEA-IRFU/CNRS/Universite Paris Diderot, Service d' Astrophysique, CEA Saclay, 91191 Gif sur Yvette (France); Barbiellini, G. [Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste (Italy); Bastieri, D. [Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova (Italy); Bignami, G. F., E-mail: digel@stanford.edu, E-mail: Gino.Tosti@pg.infn.it, E-mail: jean.ballet@cea.fr, E-mail: tburnett@u.washington.edu [Istituto Universitario di Studi Superiori (IUSS), I-27100 Pavia (Italy); and others
2012-04-01
We present the second catalog of high-energy {gamma}-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24 month period. The second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are flux measurements in five energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. We provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we attach caution flags to 162 of the sources to indicate possible confusion with residual imperfections in the diffuse model. The 2FGL catalog contains 1873 sources detected and characterized in the 100 MeV to 100 GeV range of which we consider 127 as being firmly identified and 1171 as being reliably associated with counterparts of known or likely {gamma}-ray-producing source classes.
Switchable Fermi surface sheets in greigite
Zhang, B.; de Wijs, G. A.; de Groot, R. A.
2012-01-01
Greigite (Fe3S4) and magnetite (Fe3O4) are isostructural and isoelectronic ferrimagnets with quite distinct properties. Electronic structure calculations reveal greigite is a normalmetal in contrast to half-metallic magnetite. Greigite shows a complex Fermi surface with a unique influence of relativ
Fermi Large Area Telescope Second Source Catalog
,
2011-01-01
We present the second catalog of high-energy gamma-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24-month period. The Second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are flux measurements in 5 energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. We provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we att...
Radiatively Induced Fermi Scale in Grand Unification
DEFF Research Database (Denmark)
Alanne, Tommi; Meroni, Aurora; Sannino, Francesco;
2016-01-01
We consider Grand Unified Theories in which the hierarchy between the unification and the Fermi scale emerges radiatively. Within the Pati-Salam framework, we show that it is possible to construct a viable model where the Higgs is an elementary pseudo-Goldstone boson, and the correct hierarchy...
Automatic Cloud Bursting under FermiCloud
Energy Technology Data Exchange (ETDEWEB)
Wu, Hao [Fermilab; Shangping, Ren [IIT; Garzoglio, Gabriele [Fermilab; Timm, Steven [Fermilab; Bernabeu, Gerard [Fermilab; Kim, Hyun Woo; Chadwick, Keith; Jang, Haengjin [KISTI, Daejeon; Noh, Seo-Young [KISTI, Daejeon
1900-01-01
Cloud computing is changing the infrastructure upon which scientific computing depends from supercomputers and distributed computing clusters to a more elastic cloud-based structure. The service-oriented focus and elasticity of clouds can not only facilitate technology needs of emerging business but also shorten response time and reduce operational costs of traditional scientific applications. Fermi National Accelerator Laboratory (Fermilab) is currently in the process of building its own private cloud, FermiCloud, which allows the existing grid infrastructure to use dynamically provisioned resources on FermiCloud to accommodate increased but dynamic computation demand from scientists in the domains of High Energy Physics (HEP) and other research areas. Cloud infrastructure also allows to increase a private cloud’s resource capacity through “bursting” by borrowing or renting resources from other community or commercial clouds when needed. This paper introduces a joint project on building a cloud federation to support HEP applications between Fermi National Accelerator Laboratory and Korea Institution of Science and Technology Information, with technical contributions from the Illinois Institute of Technology. In particular, this paper presents two recent accomplishments of the joint project: (a) cloud bursting automation and (b) load balancer. Automatic cloud bursting allows computer resources to be dynamically reconfigured to meet users’ demands. The load balance algorithm which the cloud bursting depends on decides when and where new resources need to be allocated. Our preliminary prototyping and experiments have shown promising success, yet, they also have opened new challenges to be studied
Automatic Cloud Bursting under FermiCloud
Energy Technology Data Exchange (ETDEWEB)
Wu, Hao [Fermilab; Shangping, Ren [IIT; Garzoglio, Gabriele [Fermilab; Timm, Steven [Fermilab; Bernabeu, Gerard [Fermilab; Kim, Hyun Woo; Chadwick, Keith; Jang, Haengjin [KISTI, Daejeon; Noh, Seo-Young [KISTI, Daejeon
2013-01-01
Cloud computing is changing the infrastructure upon which scientific computing depends from supercomputers and distributed computing clusters to a more elastic cloud-based structure. The service-oriented focus and elasticity of clouds can not only facilitate technology needs of emerging business but also shorten response time and reduce operational costs of traditional scientific applications. Fermi National Accelerator Laboratory (Fermilab) is currently in the process of building its own private cloud, FermiCloud, which allows the existing grid infrastructure to use dynamically provisioned resources on FermiCloud to accommodate increased but dynamic computation demand from scientists in the domains of High Energy Physics (HEP) and other research areas. Cloud infrastructure also allows to increase a private cloud’s resource capacity through “bursting” by borrowing or renting resources from other community or commercial clouds when needed. This paper introduces a joint project on building a cloud federation to support HEP applications between Fermi National Accelerator Laboratory and Korea Institution of Science and Technology Information, with technical contributions from the Illinois Institute of Technology. In particular, this paper presents two recent accomplishments of the joint project: (a) cloud bursting automation and (b) load balancer. Automatic cloud bursting allows computer resources to be dynamically reconfigured to meet users’ demands. The load balance algorithm which the cloud bursting depends on decides when and where new resources need to be allocated. Our preliminary prototyping and experiments have shown promising success, yet, they also have opened new challenges to be studied
Fermi Large Area Telescope Second Source Catalog
Nolan, P. L.; Abdo, A. A.; Ackermann, M.; Ajello, M; Allafort, A.; Antolini, E; Bonnell, J.; Cannon, A.; Celik O.; Corbet, R.; Davis, D. S.; DeCesar, M. E.; Ferrara, E. C.; Gehrels, N.; Harding, A. K.; Hays, E.; Johnson, T. E.; McConville, W.; McEnery, J. E; Perkins, J. S.; Racusin, J. L; Scargle, J. D.; Stephens, T. E.; Thompson, D. J.; Troja, E.
2012-01-01
We present the second catalog of high-energy gamma-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24-month period. The Second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are flux measurements in 5 energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. We provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we attach caution flags to 162 of the sources to indicate possible confusion with residual imperfections in the diffuse model. The 2FGL catalog contains 1873 sources detected and characterized in the 100 11eV to 100 GeV range of which we consider 127 as being firmly identified and 1171 as being reliably associated with counterparts of known or likely gamma-ray-producing source classes.
76 FR 1197 - Detroit Edison Company, FERMI 2; Exemption
2011-01-07
... COMMISSION Detroit Edison Company, FERMI 2; Exemption 1.0 Background Detroit Edison Company (DECo) (the licensee) is the holder of Facility Operating License No. NFP-43 which authorizes operation of the Fermi 2... exemption stated that a tornado swept across the Fermi 2 property on June 6, 2010, and that the...
75 FR 15748 - Detroit Edison Company; Fermi 2; Exemption
2010-03-30
... COMMISSION Detroit Edison Company; Fermi 2; Exemption 1.0 Background Detroit Edison Company (the licensee) is the holder of Facility Operating License No. NPF-43, which authorizes operation of Fermi 2. The...- September 11, 2001, security orders. It is from five of these new requirements that Fermi 2 now seeks...
Desulphurization of exhaust gases in chemical processes
Energy Technology Data Exchange (ETDEWEB)
Asperger, K.; Wischnewski, W.
1981-01-01
The sulfur content of exhaust gases can be reduced by: desulphurization of fuels; modification of processes; or treatment of resultant gases. In this paper a few selected examples from the chemical industry in the German Democratic Republic are presented. Using modified processes and treating the resultant gases, the sulphuric content of exhaust gases is effectively reduced. Methods to reduce the sulfur content of exhaust gases are described in the field of production of: sulphuric acid; viscose; fertilizers; and paraffin.
Scattering in Quantum Lattice Gases
O'Hara, Andrew; Love, Peter
2009-03-01
Quantum Lattice Gas Automata (QLGA) are of interest for their use in simulating quantum mechanics on both classical and quantum computers. QLGAs are an extension of classical Lattice Gas Automata where the constraint of unitary evolution is added. In the late 1990s, David A. Meyer as well as Bruce Boghosian and Washington Taylor produced similar models of QLGAs. We start by presenting a unified version of these models and study them from the point of view of the physics of wave-packet scattering. We show that the Meyer and Boghosian-Taylor models are actually the same basic model with slightly different parameterizations and limits. We then implement these models computationally using the Python programming language and show that QLGAs are able to replicate the analytic results of quantum mechanics (for example reflected and transmitted amplitudes for step potentials and the Klein paradox).
Bang, Jeongho; Yoo, Seokwon
2014-01-01
We propose a genetic-algorithm-based method to find the unitary transformations for any desired quantum computation. We formulate a simple genetic algorithm by introducing the "genetic parameter vector" of the unitary transformations to be found. In the genetic algorithm process, all components of the genetic parameter vectors are supposed to evolve to the solution parameters of the unitary transformations. We apply our method to find the optimal unitary transformations and to generalize the ...
Jiang, Xiu-lan; Sun, Cheng-lin; Zhou, Mi; Li, Dong-fei; Men, Zhi-wei; Li, Zuo-wei; Gao, Shu-qin
2015-03-01
Fermi resonance is a phenomenon of molecular vibrational coupling and energy transfer occurred between different groups of a single molecule or neighboring molecules. Many properties of Fermi resonance under different external fields, the investigation method of Raman spectroscopy as well as the application of Fermi resonance, etc need to be developed and extended further. In this article the research results and development about Fermi resonance obtained by Raman spectral technique were introduced systematically according to our work and the results by other researchers. Especially, the results of the behaviors of intramolecular and intermolecular Fermi resonance of some molecules under some external fields such as molecular field, pressure field and temperature field, etc were investigated and demonstrated in detail according to the Raman spectra obtained by high pressure DAC technique, temperature variation technique as well as the methods we planed originally in our group such as solution concentration variation method and LCOF resonance Raman spectroscopic technique, and some novel properties of Fermi resonance were found firstly. Concretely, (1) Under molecular field. a. The Raman spectra of C5H5 N in CH3 OH and H2O indicates that solvent effect can influence Fermi resonance distinctly; b. The phenomena of the asymmetric movement of the Fermi resonance doublets as well as the fundamental involved is tuned by the Fermi resonance which had not been found by other methods were found firstly by our variation solution concentration method; c. The Fermi resonance properties can be influenced distinctly by the molecular group reorganization induced by the hydrogen bond and anti-hydrogen bond in solution; d. Fermi resonance can occurred between C7 H8 and m-C8H10, and the Fermi resonance properties behave quite differently with the solution concentration; (2) Under pressure field. a. The spectral lines shift towards high wavenumber with increasing pressure, and
Quantum Control nd Measurement of Spins in Cold Atomic Gases
Deutsch, Ivan
2014-03-01
Spins are natural carriers of quantum information given their long coherence time and our ability to precisely control and measure them with magneto-optical fields. Spins in cold atomic gases provide a pristine environment for such quantum control and measurement, and thus this system can act as a test-bed for the development of quantum simulators. I will discuss the progress my group has made in collaboration with Prof. Jessen, University of Arizona, to develop the toolbox for this test-bed. Through its interactions with rf and microwave magnetic fields, whose waveforms are designed through optimal control techniques, we can implement arbitrary unitary control on the internal hyperfine spins of cesium atoms, a 16 dimensional Hilbert space (isomorphic to 4 qubits). Control of the collective spin of the ensemble of many atoms is performed via the mutual coupling of the atomic ensemble to a mode of the electromagnetic field that acts as a quantum data bus for entangling atoms with one another. Internal spin control can be used to enhance the entangling power of the atom-photon interface. Finally, both projective and weak-continuous measurements can be performed to tomograhically reconstruct quantum states and processes.
Phonon contribution to the shear viscosity of a superfluid Fermi gas in the unitarity limit
Energy Technology Data Exchange (ETDEWEB)
Mannarelli, Massimo [I.N.F.N., Laboratori Nazionali del Gran Sasso, Assergi (AQ) (Italy); Manuel, Cristina [Instituto de Ciencias del Espacio (IEEC/CSIC), Campus Universitat Autònoma de Barcelona, Facultat de Ciències, Torre C5, E-08193 Bellaterra (Barcelona) (Spain); Tolos, Laura, E-mail: tolos@ice.csic.es [Instituto de Ciencias del Espacio (IEEC/CSIC), Campus Universitat Autònoma de Barcelona, Facultat de Ciències, Torre C5, E-08193 Bellaterra (Barcelona) (Spain); Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe University, Ruth-Moufang-Str. 1, 60438 Frankfurt am Main (Germany)
2013-09-15
We present a detailed analysis of the contribution of small-angle Nambu–Goldstone boson (phonon) collisions to the shear viscosity, η, in a superfluid atomic Fermi gas close to the unitarity limit. We show that the experimental values of the shear viscosity coefficient to entropy ratio, η/s, obtained at the lowest reached temperature can be reproduced assuming that phonons give the leading contribution to η. The phonon contribution is evaluated considering 1↔2 processes and taking into account the finite size of the experimental system. In particular, for very low temperatures, T≲0.1T{sub F}, we find that phonons are ballistic and the contribution of phonons to the shear viscosity is determined by the processes that take place at the interface between the superfluid and the normal phase. This result is independent of the detailed form of the phonon dispersion law and leads to two testable predictions: the shear viscosity should correlate with the size of the optical trap and it should decrease with decreasing temperature. For higher temperatures the detailed form of the phonon dispersion law becomes relevant and, within our model, we find that the experimental data for η/s can be reproduced assuming that phonons have an anomalous dispersion law. -- Highlights: •We study the contribution of phonons to shear viscosity of a cold Fermi gas at unitary. •The shear viscosity to entropy ratio (η/s) is reproduced for T<∼0.1T{sub F}. •For very low temperatures η/s correlates with the size of the optical trap. •We explain η/s for T>∼0.1T{sub F} assuming an anomalous dispersion law for phonons.
Nonequilibrium steady states of ideal bosonic and fermionic quantum gases
Vorberg, Daniel; Wustmann, Waltraut; Schomerus, Henning; Ketzmerick, Roland; Eckardt, André
2015-12-01
We investigate nonequilibrium steady states of driven-dissipative ideal quantum gases of both bosons and fermions. We focus on systems of sharp particle number that are driven out of equilibrium either by the coupling to several heat baths of different temperature or by time-periodic driving in combination with the coupling to a heat bath. Within the framework of (Floquet-)Born-Markov theory, several analytical and numerical methods are described in detail. This includes a mean-field theory in terms of occupation numbers, an augmented mean-field theory taking into account also nontrivial two-particle correlations, and quantum-jump-type Monte Carlo simulations. For the case of the ideal Fermi gas, these methods are applied to simple lattice models and the possibility of achieving exotic states via bath engineering is pointed out. The largest part of this work is devoted to bosonic quantum gases and the phenomenon of Bose selection, a nonequilibrium generalization of Bose condensation, where multiple single-particle states are selected to acquire a large occupation [Phys. Rev. Lett. 111, 240405 (2013), 10.1103/PhysRevLett.111.240405]. In this context, among others, we provide a theory for transitions where the set of selected states changes, describe an efficient algorithm for finding the set of selected states, investigate beyond-mean-field effects, and identify the dominant mechanisms for heat transport in the Bose-selected state.
Nonequilibrium steady states of ideal bosonic and fermionic quantum gases.
Vorberg, Daniel; Wustmann, Waltraut; Schomerus, Henning; Ketzmerick, Roland; Eckardt, André
2015-12-01
We investigate nonequilibrium steady states of driven-dissipative ideal quantum gases of both bosons and fermions. We focus on systems of sharp particle number that are driven out of equilibrium either by the coupling to several heat baths of different temperature or by time-periodic driving in combination with the coupling to a heat bath. Within the framework of (Floquet-)Born-Markov theory, several analytical and numerical methods are described in detail. This includes a mean-field theory in terms of occupation numbers, an augmented mean-field theory taking into account also nontrivial two-particle correlations, and quantum-jump-type Monte Carlo simulations. For the case of the ideal Fermi gas, these methods are applied to simple lattice models and the possibility of achieving exotic states via bath engineering is pointed out. The largest part of this work is devoted to bosonic quantum gases and the phenomenon of Bose selection, a nonequilibrium generalization of Bose condensation, where multiple single-particle states are selected to acquire a large occupation [Phys. Rev. Lett. 111, 240405 (2013)]. In this context, among others, we provide a theory for transitions where the set of selected states changes, describe an efficient algorithm for finding the set of selected states, investigate beyond-mean-field effects, and identify the dominant mechanisms for heat transport in the Bose-selected state.
Explosion limits for combustible gases
Institute of Scientific and Technical Information of China (English)
TONG Min-ming; WU Guo-qing; HAO Ji-fei; DAI Xin-lian
2009-01-01
Combustible gases in coal mines are composed of methane, hydrogen, some multi-carbon alkane gases and other gases. Based on a numerical calculation, the explosion limits of combustible gases were studied, showing that these limits are related to the concentrations of different components in the mixture. With an increase of C4H10 and C6H14, the Lower ExplosionLimit (LEL) and Upper Explosion-Limit (UEL) of a combustible gas mixture will decrease clearly. For every 0.1% increase in C4H10 and C6H14, the LEL decreases by about 0.19% and the UEL by about 0.3%. The results also prove that, by increasing the amount of H2, the UEL of a combustible gas mixture will increase considerably. If the level of H2 increases by 0.1%, the UEL will increase by about 0.3%. However, H2 has only a small effect on the LEL of the combustible gas mixture. Our study provides a theoretical foundation for judging the explosion risk of an explosive gas mixture in mines.
Hydrophobic encapsulation of hydrocarbon gases.
Leontiev, Alexander V; Saleh, Anas W; Rudkevich, Dmitry M
2007-04-26
[reaction: see text] Encapsulation data for hydrophobic hydrocarbon gases within a water-soluble hemicarcerand in aqueous solution are reported. It is concluded that hydrophobic interactions serve as the primary driving force for the encapsulation, which can be used for the design of gas-separating polymers with intrinsic inner cavities.
The basis of the Fermi liquid theory
Apostol, M
2001-01-01
Interaction may affect drastically the many-particle ensembles; for instance an attraction, even weak, between electrons, binds them up in pairs, leading to superconductivity; interacting fermions in one dimension get bosonized; anisotropic fermions with 'nested' Fermi surfaces become non-homogeneous, when interacting, and develop charge- or spin- density waves. All these are different phases, and appear as symmetry breakings, spontaneous or induced; they are also termed as instabilities of the many-body systems, under interaction. Hints toward their nature are often obtained through studying the interacting two-particle problem, scattering included. In this paper the basis of the Fermi liquid theory is shown, and electronic liquid is briefly discussed. (author)
Quantum gravity as a Fermi liquid
Alexander, Stephon H S
2008-01-01
We present a reformulation of loop quantum gravity with a cosmological constant and no matter as a Fermi-liquid theory. When the topological sector is deformed and large gauge symmetry is broken, we show that the Chern-Simons state reduces to Jacobson's degenerate sector describing 1+1 dimensional propagating fermions with nonlocal interactions. The Hamiltonian admits a dual description which we realize in the simple BCS model of superconductivity. On one hand, Cooper pairs are interpreted as wormhole correlations at the de Sitter horizon; their number yields the de Sitter entropy. On the other hand, BCS is mapped into a deformed conformal field theory reproducing the structure of quantum spin networks. When area measurements are performed, Cooper-pair insertions are activated on those edges of the spin network intersecting the given area, thus providing a description of quantum measurements in terms of excitations of a Fermi sea to superconducting levels. The cosmological constant problem is naturally addres...
Relativistic Beaming Effect in Fermi Blazars
Indian Academy of Sciences (India)
J. H. Fan; D. Bastieri; J. H. Yang; Y. Liu; D. X. Wu; S. H. Li
2014-09-01
The most identified sources observed by Fermi/LAT are blazars, based on which we can investigate the emission mechanisms and beaming effect in the -ray bands for blazars. Here, we used the compiled around 450 Fermi blazars with the available X-ray observations to estimate their Doppler factors and compared them with the integral -ray luminosity in the range of 1–100 GeV. It is interesting that the integral -ray luminosity is closely correlated with the estimated Doppler factor, log = (2.95 ± 0.09) log + 43.59 ± 0.08 for the whole sample. When the dependence of the correlation between them and the X-ray luminosity is removed, the correlation is still strong, which suggests that the -ray emissions are strongly beamed.
Magnetar Observations in the Fermi Era
Kouveliotou, Chryssa
2009-01-01
NASA s Fermi Observatory was launched June 11, 2009; the Fermi Gamma Ray Burst Monitor (GBM) began normal operations on July 14, about a month after launch, when the trigger algorithms were enabled. In the first 8 months of operations we recorded emission of three magnetar sources; of these, only one was an old magnetar: SGR 1806+20. The other two detections were: SGR J0501+4516, newly discovered with Swift and extensively monitored with both Swift and GBM, and SGR J1550-5418, a source originally classified as an Anomalous X-ray Pulsar (AXP). I report below on the current status of the analyses efforts of all these GBM data sets, combined with data from other satellites (Spitzer, RXTE, Chandra, Swift).
Magnetar Observations with Fermi/GBM
Kouveliotou, Chryssa
2009-01-01
NASA's Fermi Observatory was launched June 11, 2009; the Fermi Gamma Ray Burst Monitor (GBM) began normal operations on July 14, about a month after launch, when the trigger algorithms were enabled. In the first year of operations we recorded emission from four magnetar sources; of these, only one was an old magnetar: SGR 1806+20. The other three detections were: SGR J0501+4516, newly discovered with Swift and extensively monitored with both Swift and GBM, SGR J1550-5418, a source originally classified as an Anomalous X-ray Pulsar (AXP) and a very recently discovered new source, SGR 0418+5729. I report below on the current status of the analyses efforts of the GBM data.
A Probabilistic Analysis of the Fermi Paradox
Solomonides, Evan; Terzian, Yervant
2016-01-01
The fermi paradox uses an appeal to the mediocrity principle to make it seem counter-intuitive that humanity has not been contacted by extraterrestrial intelligence. A numerical, statistical analysis was conducted to determine whether this apparent loneliness is, in fact, unexpected. An inequality was derived to relate the frequency of life arising and developing technology on a suitable planet in the galaxy, the average length of time since the first broadcast of such a civilization, and a constant term. An analysis of the sphere reached thus far by human communication was also conducted, considering our local neighborhood and planets of particular interest. We clearly show that human communication has not reached a number of stars and planets adequate to expect an answer. These analyses both conclude that the Fermi paradox is not, in fact, unexpected. By the mediocrity principle and numerical modeling, it is actually unlikely that the Earth would have been reached by extraterrestrial communication at this p...
Unconventional Fermi surface in an insulating state
Energy Technology Data Exchange (ETDEWEB)
Harrison, Neil [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Tan, B. S. [Cambridge Univ., Cambridge (United Kingdom); Hsu, Y. -T. [Cambridge Univ., Cambridge (United Kingdom); Zeng, B. [National High Magnetic Field Lab., Tallahassee, FL (United States); Hatnean, M. Ciomaga [Univ. of Warwick, Coventry (United Kingdom); Zhu, Z. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Hartstein, M. [Cambridge Univ., Cambridge (United Kingdom); Kiourlappou, M. [Cambridge Univ., Cambridge (United Kingdom); Srivastava, A. [Cambridge Univ., Cambridge (United Kingdom); Johannes, M. D. [Center for Computational Materials Science, Washington, DC (United States); Murphy, T. P. [National High Magnetic Field Lab., Tallahassee, FL (United States); Park, J. -H. [National High Magnetic Field Lab., Tallahassee, FL (United States); Balicas, L. [National High Magnetic Field Lab., Tallahassee, FL (United States); Lonzarich, G. G. [Cambridge Univ., Cambridge (United Kingdom); Balakrishnan, G. [Univ. of Warwick, Coventry (United Kingdom); Sebastian, Suchitra E. [Cambridge Univ., Cambridge (United Kingdom)
2015-07-17
Insulators occur in more than one guise; a recent finding was a class of topological insulators, which host a conducting surface juxtaposed with an insulating bulk. Here, we report the observation of an unusual insulating state with an electrically insulating bulk that simultaneously yields bulk quantum oscillations with characteristics of an unconventional Fermi liquid. We present quantum oscillation measurements of magnetic torque in high-purity single crystals of the Kondo insulator SmB_{6}, which reveal quantum oscillation frequencies characteristic of a large three-dimensional conduction electron Fermi surface similar to the metallic rare earth hexaborides such as PrB_{6} and LaB_{6}. As a result, the quantum oscillation amplitude strongly increases at low temperatures, appearing strikingly at variance with conventional metallic behavior.