Theory of remote entanglement via quantum-limited phase-preserving amplification

We show that a quantum-limited phase-preserving amplifier can act as a which-path information eraser when followed by heterodyne detection. This 'beam splitter with gain' implements a continuous joint measurement on the signal sources. As an application, we propose heralded concurrent remote entanglement generation between two qubits coupled dispersively to separate cavities. Dissimilar qubit-cavity pairs can be made indistinguishable by simple engineering of the cavity driving fields providing further experimental flexibility and the prospect for scalability. Additionally, we find an analytic solution for the stochastic master equation, a quantum filter, yielding a thorough physical understanding of the nonlinear measurement process leading to an entangled state of the qubits. We determine the concurrence of the entangled states and analyze its dependence on losses and measurement inefficiencies.Comment: Main text (11 pages, 5 figures), updated to the published versio

A Review of Magnetic Resonance Spectroscopy Studies in Marijuana using Adolescents and Adults

Marijuana (MJ) remains the most widely used illicit drug of abuse, and accordingly, is associated with adverse effects on mental and physical health, and neurocognitive decline. Studies investigating the neurobiology of underlying MJ effects have demonstrated structural and functional alterations in brain areas that contain moderate to high concentrations of cannabinoid (CB1) receptors and that are implicated in MJ-related cognitive decrements. Proton magnetic resonance spectroscopy (1H MRS), a non-invasive imaging technique used to assess neurochemistry, has been widely applied to probe a variety of substance-abusing populations. To date, however, there is a relative paucity of MRS published studies characterizing changes in neurometabolite concentrations in MJ users. Thus, the current review provides a summary of data from the eight existing MRS studies of MJ use in adolescents and adults, as well as interpretations and implications of study findings. Future MRS studies that address additional factors such as sex differences, onset and duration of use, abstinence and age, are warranted, and would lead to a more thorough characterization of potential neurochemical correlates of chronic MJ use, which would fill critical gaps in the existing literature

New class of quantum error-correcting codes for a bosonic mode

We construct a new class of quantum error-correcting codes for a bosonic mode which are advantageous for applications in quantum memories, communication, and scalable computation. These 'binomial quantum codes' are formed from a finite superposition of Fock states weighted with binomial coefficients. The binomial codes can exactly correct errors that are polynomial up to a specific degree in bosonic creation and annihilation operators, including amplitude damping and displacement noise as well as boson addition and dephasing errors. For realistic continuous-time dissipative evolution, the codes can perform approximate quantum error correction to any given order in the timestep between error detection measurements. We present an explicit approximate quantum error recovery operation based on projective measurements and unitary operations. The binomial codes are tailored for detecting boson loss and gain errors by means of measurements of the generalized number parity. We discuss optimization of the binomial codes and demonstrate that by relaxing the parity structure, codes with even lower unrecoverable error rates can be achieved. The binomial codes are related to existing two-mode bosonic codes but offer the advantage of requiring only a single bosonic mode to correct amplitude damping as well as the ability to correct other errors. Our codes are similar in spirit to 'cat codes' based on superpositions of the coherent states, but offer several advantages such as smaller mean number, exact rather than approximate orthonormality of the code words, and an explicit unitary operation for repumping energy into the bosonic mode. The binomial quantum codes are realizable with current superconducting circuit technology and they should prove useful in other quantum technologies, including bosonic quantum memories, photonic quantum communication, and optical-to-microwave up- and down-conversion.Comment: Published versio

Stark effect and generalized Bloch-Siegert shift in a strongly driven two-level system

A superconducting qubit was driven in an ultrastrong fashion by an oscillatory microwave field, which was created by coupling via the nonlinear Josephson energy. The observed Stark shifts of the `atomic' levels are so pronounced that corrections even beyond the lowest-order Bloch-Siegert shift are needed to properly explain the measurements. The quasienergies of the dressed two-level system were probed by resonant absorption via a cavity, and the results are in agreement with a calculation based on the Floquet approach.Comment: 4+ page

Implementing and characterizing precise multi-qubit measurements

There are two general requirements to harness the computational power of quantum mechanics: the ability to manipulate the evolution of an isolated system and the ability to faithfully extract information from it. Quantum error correction and simulation often make a more exacting demand: the ability to perform non-destructive measurements of specific correlations within that system. We realize such measurements by employing a protocol adapted from [S. Nigg and S. M. Girvin, Phys. Rev. Lett. 110, 243604 (2013)], enabling real-time selection of arbitrary register-wide Pauli operators. Our implementation consists of a simple circuit quantum electrodynamics (cQED) module of four highly-coherent 3D transmon qubits, collectively coupled to a high-Q superconducting microwave cavity. As a demonstration, we enact all seven nontrivial subset-parity measurements on our three-qubit register. For each we fully characterize the realized measurement by analyzing the detector (observable operators) via quantum detector tomography and by analyzing the quantum back-action via conditioned process tomography. No single quantity completely encapsulates the performance of a measurement, and standard figures of merit have not yet emerged. Accordingly, we consider several new fidelity measures for both the detector and the complete measurement process. We measure all of these quantities and report high fidelities, indicating that we are measuring the desired quantities precisely and that the measurements are highly non-demolition. We further show that both results are improved significantly by an additional error-heralding measurement. The analyses presented here form a useful basis for the future characterization and validation of quantum measurements, anticipating the demands of emerging quantum technologies.Comment: 10 pages, 5 figures, plus supplemen

Spatial and seasonal distribution of invertebrates in Northern Apennine rheocrene springs

Four perennial rheocrene springs located between 919 and 1252 m a.s.l. on substrata characterized by different lithologies were studied. Water samples and invertebrates were collected seasonally for one year. The crenic fauna was collected using three sampling techniques: moss washing, drift tubes and benthic traps. Each sampling technique was particularly efficient for collecting specific taxa typical of the different habitats (crenophilous crustaceans and crenoxenic benthic insects were dominant in benthic traps and moss; crenophilic, stygophilic and stygobiotic crustaceans in drift tubes). A total of 3,284 invertebrates belonging to 54 taxa were collected. Ostracoda, Harpacticoida, and Diptera were the most abundant taxa. Species assemblages collected at each spring, in each season, in traps and mosses, differed among springs, and, based on invertebrate assemblages, the ordination of the investigated springs did not correspond to that based on environmental parameters. Of the environmental variables only pH and temperature explained the diversity pattern. Assemblages collected from different habitats also differed: benthic traps collected mainly Chironomidae, Ostracoda, other Diptera, crenophilous Harpacticoida, and Gastropoda; in moss assemblages, the fauna was mostly represented by crenophilic Harpacticoida, Ostracoda, Plecoptera, Chironomidae. Finally, the groundwater assemblages, collected with drift tubes, were dominated by crenophilous Harpacticoida, Chironomidae and Plecoptera. Variation in number of taxa over time was observed in traps and moss samples, whereas drift tubes showed no seasonality. Meiofauna (i.e., permanent meiofauna, represented by Nematoda, Copepoda, Ostracoda, and Hydrachnidia, and temporary meiofauna, represented by early instars of insect larvae) dominated all habitats, probably because of constant flow and favourable habitats such as moss. The presence of mosses was a factor that increased the species diversity of the investigated springs; drift tubes allowed most of the stygobiotic taxa to be collected, although this technique did not necessarily increase the total number of taxa collected. In addition to the array of habitats, other factors, such as geology, might influence the structure of invertebrate communities. The diversity of the investigated springs was strictly dependent on the presence of different microhabitats and local environmental conditions

Lower Left Thalamic Myo-Inositol Levels Associated with Greater Cognitive Impulsivity in Marijuana-Dependent Young Men: Preliminary Spectroscopic Evidence at 4T

The effects of chronic marijuana (MRJ) use on neurochemistry are not well characterized. Previously, altered global myo-Inositol (mI) concentrations and distribution in white matter were associated with impulsivity and mood symptoms in young MRJ-dependent men. The objective of this study was to retrospectively examine previously collected data, to investigate the potential regional specificity of metabolite levels in brain regions densely packed with cannabinoid receptors. Spectra were acquired at 4.0 Tesla using 2D J-resolved proton magnetic resonance spectroscopic imaging (MRSI) to quantify the entire J-coupled spectral surface of metabolites from voxels in regions of interest. For the current regional spectral analyses, a 2D-JMRSI grid was positioned over the central axial slice and shifted in the x and y dimensions to optimally position voxels over regions containing thalamus, temporal lobe, and parieto-occipital cortex. MRJ users exhibited significantly reduced mI levels in the left thalamus (lThal), relative to non-using participants, which were associated with elevated cognitive impulsivity. Other regional analyses did not reveal any significant group differences. The current findings indicate that reduced mI levels are regionally specific to the lThal in MRJ users. Furthermore, findings suggest that mI and the lThal uniquely contribute to elevated impulsivity

Gitelman syndrome associated with chondrocalcinosis: description of two cases

Gitelman syndrome is a rare inherited tubulopathy, characterized by hypomagnesemia, hypokalemia, metabolic alkalosis, hypocalciuria and hyperreninemic hyperaldosteronism. The clinical spectrum is wide and includes: cramps, myalgies, muscle weakness, until episodes of carpo-podalic spasm, tetania, rabdomyolisis and paralysis. Some cases have been described in literature underlining the association of this condition with chondrocalcinosis, as a typical example of hypomagnesemia-induced crystal deposition disease. The therapy of Gitelman syndrome consists on the administration of defective electrolytes, althought not always effective. We describe two cases of Gitelman syndrome associated with chondrocalcinosis showing the wide range of presentation of this clinical condition

Effects of Yoga on Thalamic Gamma-Aminobutyric Acid, Mood and Depression: Analysis of Two Randomized Controlled Trials

Objective: The Vagal-Gamma-Aminobutyric Acid (GABA) theory proposes that some yoga postures and breathing practices exert their effects through stimulation of vagal nerves (parasympathetic system) with associated brain GABA increases. To evaluate this theory, we compared results from a 12-week randomized controlled trial (RCT) of yoga in participants with Major Depressive Disorder (MDD) with those of a similar RCT in healthy control participants (HC). Methods: In an RCT, magnetic resonance spectroscopy (MRS) and mood measures were acquired in subjects with MDD (n=15) prior to and following a 12-week yoga intervention. The same measures were obtained in the HC (n=17) group. In both studies, thalamic GABA/Creatine was obtained using MEGAPRESS at 4 Telsa at baseline (Scan-1), post-intervention (Scan-2), and immediately following a yoga session (Scan-3). Clinical scales were completed prior to each scan. Results: The MDD-group had significantly lower GABA compared to the HC at baseline (Scan-1, p=0.001), but not after 12 weeks of yoga, either before (Scan-2, p=0.12) or after a yoga session (Scan-3, p=0.20). Depressive symptoms decreased significantly in the MDD-group (p=0.0001), and anxiety improved in both groups. Conclusion: After a 12-week yoga intervention, MDD-group mood and anxiety measures improved with scores equivalent to those of non-depressed individuals. This study provides the first evidence of brain GABA increases associated with specific yoga postures and breathing practices in MDD. These results suggest potential benefits of specific yoga postures and breathing practices as monotherapy or augmentation to other treatments to reduce anxiety and depression in MDD