Symmetry Breaking and Error Correction in Open Quantum Systems

Symmetry-breaking transitions are a well-understood phenomenon of closed quantum systems in quantum optics, condensed matter, and high energy physics. However, symmetry breaking in open systems is less thoroughly understood, in part due to the richer steady-state and symmetry structure that such systems possess. For the prototypical open system—a Lindbladian—a unitary symmetry can be imposed in a “weak” or a “strong” way. We characterize the possible Z_n symmetry-breaking transitions for both cases. In the case of Z₂, a weak-symmetry-broken phase guarantees at most a classical bit steady-state structure, while a strong-symmetry-broken phase admits a partially protected steady-state qubit. Viewing photonic cat qubits through the lens of strong-symmetry breaking, we show how to dynamically recover the logical information after any gap-preserving strong-symmetric error; such recovery becomes perfect exponentially quickly in the number of photons. Our study forges a connection between driven-dissipative phase transitions and error correction

Symmetry breaking and error correction in open quantum systems

Symmetry-breaking transitions are a well-understood phenomenon of closed quantum systems in quantum optics, condensed matter, and high energy physics. However, symmetry breaking in open systems is less thoroughly understood, in part due to the richer steady-state and symmetry structure that such systems possess. For the prototypical open system---a Lindbladian---a unitary symmetry can be imposed in a "weak" or a "strong" way. We characterize the possible $\mathbb{Z}_n$ symmetry breaking transitions for both cases. In the case of $\mathbb{Z}_2$, a weak-symmetry-broken phase guarantees at most a classical bit steady-state structure, while a strong-symmetry-broken phase admits a partially-protected steady-state qubit. Viewing photonic cat qubits through the lens of strong-symmetry breaking, we show how to dynamically recover the logical information after any gap-preserving strong-symmetric error; such recovery becomes perfect exponentially quickly in the number of photons. Our study forges a connection between driven-dissipative phase transitions and error correction.Comment: 5 + 6 page

Occurrence of White Grubs in Groundnut Crop in Uplands of South Vietnam: A New Report

Groundnut (Arachis hypogaea) is an important crop in South Vietnam covering more than 125,000 ha under different cropping systems. Crop surveys, and the onfarm research organized in Trang Bang, Cuchi, Duc Hoa and Go Dau during the past (until 2000), brought out the importance of the foliage feeding insect pests (Spodoptera, Helicoverpa) as economically important in farmers’ fields (Ranga Rao 1995). Field visits during the last week of May 2004 and interactions with the farmers in Tra Vinh province, villages around Cau Ngang town revealed the occurrence and importance of white grubs in this region. This soil-inhabiting pest is a menace in this area, which is in the heart of Mekong delta mostly covered by irrigated rice (Oryza sativa) cultivation with multiple cropping system

Assessment of Aspergillus flavus Infection and Aflatoxin Contamination in Groundnut in Southern Vietnam

Groundnut is an important food and cash crop in Vietnam with a high export potential. Limited studies of foods in the country have indicated that aflatoxin contamination is a problem in groundnut and maize. Vietnam considers the aflatoxin problem in groundnut to be of great importance, especially in view of Vietnam's expanding trade in this commodity, and the increasing use of groundnut cake as animal feed, Systematic surveys were conducted to assess Aspergillus flevus infection and aflatoxin contamination in groundnuts from farmers' fields and marketsloil mills in the major groundnut-growing areas of southern Vietnam. Results indicated that preharvest aflatoxin contamination is not likely to be a serious problem in adequately irrigated groundnuts. However, groundnuts grown under residual moisture or limited irrigation can be contaminated under conducive environmental conditions prevailing in the winter-spring season as evidenced by moderate to high aflatoxin levels found in some samples. Soilborne diseases such as stemlpod rot and bacterial wilt prevalent in many parts of southern Vietnam are likely to encourage A. flavus invasion of podlseed in the field. It is emphasized that the aflatoxin problem should be viewed holistically as contamination can be pre- and postharvest with many factors influencing, e,g., the crop rotation, soil moisture, soilborne pests and diseases, crop produce drying and storage conditions. A brochure on "Aflatoxin contamination problems in groundnuts and groundnut products" was prepared (in English and Vietnamese) and distributed to many farmers, traders, and extension and research workers to enhance awareness of the aflatoxin problem and management option

Fluid phonons and inflaton quanta at the protoinflationary transition

Quantum and thermal fluctuations of an irrotational fluid are studied across the transition regime connecting a protoinflationary phase of decelerated expansion to an accelerated epoch driven by a single inflaton field. The protoinflationary inhomogeneities are suppressed when the transition to the slow roll phase occurs sharply over space-like hypersurfaces of constant energy density. If the transition is delayed, the interaction of the quasi-normal modes related, asymptotically, to fluid phonons and inflaton quanta leads to an enhancement of curvature perturbations. It is shown that the dynamics of the fluctuations across the protoinflationary boundaries is determined by the monotonicity properties of the pump fields controlling the energy transfer between the background geometry and the quasi-normal modes of the fluctuations. After corroborating the analytical arguments with explicit numerical examples, general lessons are drawn on the classification of the protoinflationary transition.Comment: 30 pages, 3 figure

Neutralinos and the Origin of Radio Halos in Clusters of Galaxies

We assume that the supersymmetric lightest neutralino is a good candidate for the CDM and explore the possibility to produce diffuse radio emission from high-energy electrons arising from the neutralino annihilation in galaxy clusters whose intracluster medium is filled with a large-scale magnetic field. We show that these electrons fit the population of seed relativistic electrons postulated in many models for the origin of cluster radio halos. For magnetic fields with central values $3 \div 30$ $\mu$G (depending on the DM profile), the population of seed relativistic electrons from neutralino annihilation can fit the radio halo spectra of Coma and 1E0657-56. The shape and the frequency extension of the radio halo spectra are connected with the mass and physical composition of the neutralino. A pure-gaugino neutralino with mass $M_{\chi} \geq 80$ GeV can reasonably fit the spectra of both Coma and 1E0657-56. This model provides a number of extra predictions that make it definitely testable. On the one hand, it agrees with the observations that {\it (i)} the radio halo is centered on the cluster dynamical center, usually coincident with the X-ray center, {\it (ii)} the radio halo surface brightness is similar to the X-ray one, and {\it (iii)} the monochromatic radio luminosity at 1.4 GHz correlates strongly with the IC gas temperature. On the other hand, the model predicts that radio halos should be present in every cluster, which is not actually observed, although the predicted radio halo luminosities can change by a large amount ($\sim 10^2 \div 10^6$), depending on the amplitude and the structure of the IC magnetic field. Also, neutral pions arising from neutralino annihilation should give rise to substantial gamma-ray emission that could be tested by the next generation gamma-ray experiments.Comment: 49 pages, 11 Figures, Latex (using epsfig), submitted to The Astrophysical Journal. submitted to The Astrophysical Journa

A new emulated Monte Carlo radiative transfer disc-wind model: X-Ray Accretion Disc-wind Emulator - XRADE

We present a new X-Ray Accretion Disc-wind Emulator (xrade) based on the 2.5D Monte Carlo radiative transfer code that provides a physically motivated, self-consistent treatment of both absorption and emission from a disc wind by computing the local ionization state and velocity field within the flow. xrade is then implemented through a process that combines X-ray tracing with supervised machine learning. We develop a novel emulation method consisting in training, validating, and testing the simulated disc-wind spectra into a purposely built artificial neural network. The trained emulator can generate a single synthetic spectrum for a particular parameter set in a fraction of a second, in contrast to the few hours required by a standard Monte Carlo radiative transfer pipeline. The emulator does not suffer from interpolation issues with multidimensional spaces that are typically faced by traditional X-ray fitting packages such as xspec. xrade will be suitable to a wide number of sources across the black hole mass, ionizing luminosity, and accretion rate scales. As an example, we demonstrate the applicability of xrade to the physical interpretation of the X-ray spectra of the bright quasar PDS 456, which hosts the best-established accretion disc wind observed to date. We anticipate that our emulation method will be an indispensable tool for the development of high-resolution theoretical models, with the necessary flexibility to be optimized for the next generation microcalorimeters onboard future missions, like X-Ray Imaging and Spectroscopy Mission (XRISM)/Resolve and Athena/X-ray Integral Field Unit (X-IFU). This tool can also be implemented across a wide variety of X-ray spectral models and beyond

Fermion-scalar interactions with domain wall fermions

Domain wall fermions are defined on a lattice with an extra direction the size of which controls the chiral properties of the theory. When gauge fields are coupled to domain wall fermions the extra direction is treated as an internal flavor space. Here it is found that this is not the case for scalar fields. Instead, the interaction takes place only along the link that connects the boundaries of the extra direction. This reveals a richness in the way different spin particles are coupled to domain wall fermions. As an application, 4-Fermi models are studied using large N techniques and the results are supported by numerical simulations with N=2. It is found that the chiral properties of domain wall fermions in these models are good across a large range of couplings and that a phase with parity-flavor broken symmetry can develop for negative bare masses if the number of sites along the extra direction is finite.Comment: LaTeX, 17 pages, 8 eps figures; comment regarding the width of Aoki phase added in sec. 3; references adde

Some doubts on the validity of the foreground Galactic contribution subtraction from microwave anisotropies

The Galactic foreground contamination in CMBR anisotropies, especially from the dust component, is not easily separable from the cosmological or extragalactic component. In this paper, some doubts will be raised concerning the validity of the methods used to date to remove Galactic dust emission in order to show that none of them achieves its goal. First, I review the recent bibliography on the topic and discuss critically the methods of foreground subtraction: the cross-correlation with templates, analysis assuming the spectral shape of the Galactic components, the "maximum entropy method", "internal linear combination", and "wavelet-based high resolution fitting of internal templates". Second, I analyse the galactic latitude dependence from WMAP data. The frequency dependence is discussed with the data in the available literature. The result is that all methods of subtracting the Galactic contamination are inaccurate. The galactic latitude dependence analysis or the frequency dependence of the anisotropies in the range 50-250 GHz put a constraint on the maximum Galactic contribution in the power spectrum to be less than a ~10% (68% C. L.) for a ~1 degree scale, and possibly higher for larger scales. The origin of most of the signal in the CMBR anisotropies is not Galactic. In any case, the subtraction of the Galaxy is not accurate enough to allow a "precision Cosmology"; other sources of contamination (extragalactic, solar system) are also present.Comment: 24 pages, 1 figure, accepted to be published in J. Astrophys. Ast