Improving the estimation of environment parameters via a two-qubit scheme

We demonstrate how using two qubits can drastically improve the estimation of environment parameters compared to using only a single qubit. The two qubits are coupled to a common harmonic oscillator environment, and the properties of the environment are imprinted upon the dynamics of the two qubits. The reduced density matrix of only one of these qubits contains a decoherence factor and an additional factor taking into account the indirect interaction induced between the qubits due to the interaction with their common environment. This additional factor can drastically improve the estimation of the environment parameters, as quantified by the quantum Fisher information. In particular, we investigate the estimation of the cutoff frequency, the coupling strength, and the temperature using our two-qubit scheme compared to simply using a single qubit. We find that the precision of the estimates can be improved by orders of magnitude.

A generalized framework for the quantum Zeno and anti-Zeno effects in the strong coupling regime

It is well known that repeated projective measurements can either slow down (the Zeno effect) or speed up (the anti-Zeno effect) quantum evolution. Until now, studies of these effects for a two-level system interacting with its environment have focused on repeatedly preparing the excited state via projective measurements. In this paper, we consider the repeated preparation of an arbitrary state of a two-level system that is interacting strongly with an environment of harmonic oscillators. To handle the strong interaction, we perform a polaron transformation and then use a perturbative approach to calculate the decay rates for the system. Upon calculating the decay rates, we discover that there is a transition in their qualitative behaviors as the state being repeatedly prepared continuously moves away from the excited state and toward a uniform superposition of the ground and excited states. Our results should be useful for the quantum control of a two-level system interacting with its environment.

The quantum Zeno and anti-Zeno effects with non-selective projective measurements

In studies of the quantum Zeno and anti-Zeno effects, it is usual to consider rapid projective measurements with equal time intervals being performed on the system to check whether or not the system is in the initial state. These projective measurements are selective measurements in the sense that the measurement results are read out and only the case where all the measurement results correspond to the initial state is considered in the analysis of the effect of the measurements. In this paper, we extend such a treatment to consider the effect of repeated non-selective projective measurements – only the final measurement is required to correspond to the initial state, while we do not know the results of the intermediate measurements. We present a general formalism to derive the effective decay rate of the initial quantum state with such nonselective measurements. Importantly, we show that there is a difference between using non-selective projective measurements and the usual approach of considering only selective measurements only if we go beyond the weak system-environment coupling regime in models other than the usual population decay models. As such, we then apply our formalism to investigate the quantum Zeno and anti-Zeno effects for three exactly solvable system-environment models: a single two-level system undergoing dephasing, a single two-level system interacting with an environment of two-level systems and a large spin undergoing dephasing. Our results show that the quantum Zeno and anti-Zeno effects in the presence of non-selective projective measurements can differ very significantly as compared to the repeated selective measurement scenario.

The quantum Zeno and anti-Zeno effects with strong system-environment coupling

To date, studies of the quantum Zeno and anti-Zeno effects focus on quantum systems that are weakly interacting with their environment. In this paper, we investigate what happens to a quantum system under the action of repeated measurements if the quantum system is strongly interacting with its environment. We consider as the quantum system a single two-level system coupled strongly to a collection of harmonic oscillators. A so-called polaron transformation is then used to make the problem in the strong system-environment coupling regime tractable. We find that the strong coupling case exhibits quantitative and qualitative differences as compared with the weak coupling case. In particular, the effective decay rate does not depend linearly on the spectral density of the environment. This then means that, in the strong coupling regime that we investigate, increasing the system-environment coupling strength can actually decrease the effective decay rate. We also consider a collection of two-level atoms coupled strongly with a common environment. In this case, we find that there are further differences between the weak and strong coupling cases since the two-level atoms can now indirectly interact with one another due to the common environment.

A general framework for the Quantum Zeno and anti-Zeno effects

Repeated measurements can slow down (the quantum Zeno effect) or speed up (the quantum anti-Zeno effect) the temporal evolution of a quantum system. In this paper, a general treatment of the quantum Zeno and anti-Zeno effects is presented which is valid for an arbitrary system-environment model in the weak system-environment coupling regime. It is shown that the effective lifetime of a quantum state that is subjected to repeated projective measurements depends on the overlap of the spectral density of the environment and a generalized ‘filter function’. This filter function depends on the system-environment Hamiltonian, the state of the environment, and the measurement being performed. Our general framework is then used to study explicitly the Zeno to anti-Zeno crossover behaviour for the spin-boson model where a single two-level system is coupled to a bosonic environment. It is possible to not only reproduce results for the usual population decay case as well as for the pure dephasing model, but to also study the regime where both decay and dephasing take place. These results are then extended to many two-level systems coupled collectively to the bosonic environment to further illustrate the importance of the correct evaluation of the effective decay rate.

The effect of state preparation in a many-body system

For a quantum system interacting with its environment, the role of state preparation is nontrivial. The reason is that before the state preparation procedure, the system and the environment are correlated. Consequently, the state preparation procedure (which acts on the system) indirectly influences the state of the environment depending on the state preparation. In this paper, we use an experimentally realizable model describing a collection of N two-level atoms coupled to a common environment to investigate the influence of the state preparation procedure. We show that the dynamical map describing the evolution of the open quantum system can depend appreciably on the state preparation procedure. Moreover, this effect can be enhanced by increasing N. Our results should be useful for quantum control and quantum tomography.

Papillary microcarcinoma of the thyroid: a clinico-pathologic and prognostic review

Papillary microcarcinoma (PMC) of the thyroid is the most common form of thyroid cancer, which usually remains clinically silent until its incidental histologic diagnosis in autopsy or surgical material. Autopsy incidence varies from 3%-36%. PMC may, however, present with clinical symptoms, the commonest of which is cervical lymphadenopathy with or without palpable thyroid nodules. Other reported presentations include cystic neck mass, pulmonary mass (es), metastases in the skull or vertebral column. The upper limit of size to define PMC is 10 mm in most studies but many studies include lesions up to 15 mm in diameter. Histologic variants include encapsulated and partially encapsulated papillary carcinoma, circumscribed microcarcinoma and occult sclerosing carcinoma. Younger age and size less than 10 mm (< 15 mm in other studies) are considered to be favorable prognostic factors. Size alone, however, cannot be regarded as a determinant of prognosis. Older age, larger tumor size, distant metastases, capsular invasion and multifocality indicate unfavorable prognosis. Loss of heterozygosity (LOH) is an infrequent finding, since small deletions may be missed by southern blot analysis. Activation of oncogenes ret and trk have been reported in papillary carcinoma. Some authors advocate conservative while others favor aggressive therapy including total thyroidectomy with or without Iodine 131ablation. Additional investigative techniques are needed to identify the subset of PMC cases with a potential for aggressive clinical course, thereby targeting more aggressive therapy to an appropriate subset of tumors.

Exon structure of the nuclear factor I DNA-binding domain from C. elegans to mammals

The Nuclear Factor I (NFI) family of DNA-binding proteins is essential for adenovirus DNA replication and the transcription of many cellular genes. Mammals have four genes encoding NFI proteins, C. elegans has only a single NFI gene, and prokaryotes have none. To assess the relationship between members of this unusually small family of transcription/replication factors, we mapped the chromosomal locations of the four murine NFI genes and analyzed the exons encoding the DNA-binding domains of the mouse, Amphioxus, and C. elegans NFI genes. The four murine NFI genes are on Chrs 4 (Nfia and Nfib), 8 (Nfix), and 10 (Nfic), suggesting early duplication of the genes and dispersal throughout the genome. The DNA-binding domains of all four NFI genes are encoded by large (532 bp) exons with identical splice acceptor and donor sites in each. In contrast, the C. elegans nfi-1 gene has four phased introns interrupting this DNA-binding, domain-encoding exon, and the last exon extends 213 bp past the splice site used in all four murine genes. In addition, the introns present in C. elegans nfi-1 are missing from the NFI genes of Amphioxus and all mammalian genomes examined. This analysis of the exon structure of the C. elegans and murine NFI genes indicates that the murine genes were probably generated by duplication of a C. elegans-like ancestral gene, but that significant changes have occurred in the genomic organization of either the C. elegans or murine NFI genes during evolution.

Nuclear factor I-mediated repression of the mouse mammary tumor virus promoter is abrogated by the coactivators p300/CBP and SRC-1

To better understand the function of nuclear factor I (NFI) proteins in transcription, we have used transient transfection assays to assess transcriptional modulation by NFI proteins on the NFI-dependent mouse mammary tumor virus (MMTV) promoter. Expression of NFI-C or NFI-X, but not NFI-A or NFI-B proteins, represses glucocorticoid induction of the MMTV promoter in HeLa cells. Repression is DNA binding-independent as a deletion construct expressing the NH2-terminal 160 residues of NFI-C represses but does not bind DNA. Repression by NFI-C is cell type-dependent and occurs in HeLa and COS-1 cells but not 293 or JEG-3 cells. NFI-C does not repress progesterone induction of the MMTV promoter in HeLa cells, suggesting that progesterone induction of the promoter differs mechanistically from glucocorticoid induction. NFI-C-mediated repression is alleviated by overexpression of glucocorticoid receptor (GR), suggesting that NFI-C represses the MMTV promoter by preventing GR function. However, repression by NFI-C occurs with only a subset of glucocorticoid-responsive promoters, as the chimeric NFIGREbeta-gal promoter that is activated by GR is not repressed by NFI-C. Since the coactivator proteins p300/CBP, SRC-1A, and RAC3 had previously been shown to function at steroid hormone-responsive promoters, we asked whether they could influence NFI-C-mediated repression of MMTV expression. Expression of p300/CBP or SRC-1A alleviates repression by NFI-C, whereas RAC3 has no effect. This abrogation of NFI-C-mediated repression by p300/CBP and SRC-1A suggests that repression by NFI-C may occur by interference with coactivator function at the MMTV promoter.

Nuclear factor I (NFI) isoforms differentially activate simple versus complex NFI-responsive promoters

Promoter-specific differences in the function of transcription factors play a central role in the regulation of gene expression. We have measured the maximal transcriptional activation potentials of nuclear factor I (NFI) proteins encoded by each of the four identified NFI genes (NFI-A, -B, -C, and -X) by transient transfection in JEG-3 cells using two model NFI-dependent promoters: 1) a simple chimeric promoter containing a single NFI-binding site upstream of the adenovirus major late promoter (NFI-Ad), and 2) the more complex mouse mammary tumor virus long terminal repeat promoter. The relative activation potentials for the NFI isoforms differed between the two promoters, with NFI-X being the strongest activator of NFI-Ad and NFI-B being the strongest activator of the MMTV promoter. To determine if these promoter-specific differences in activation potential were due to the presence of glucocorticoid response elements (GREs), we added GREs upstream of the NFI-binding site in NFI-Ad. NFI-X remains the strongest activator of the GRE containing simple promoter, indicating that differences in relative activation potential are not due solely to the presence of GREs. Since NFI proteins bind to DNA as dimers, we assessed the activation potentials of NFI heterodimers. Here, we show that NFI heterodimers have intermediate activation potentials compared with homodimers, demonstrating one potential mechanism by which different NFI proteins can regulate gene expression.

Expression patterns of the four nuclear factor I genes during mouse embryogenesis indicate a potential role in development

The nuclear factor I (NFI) family of site-specific DNA-binding proteins is required for both the cell-type specific transcription of many viral and cellular genes and for the replication of adenovirus DNA. Although binding sites for NFI proteins within the promoters of several tissue-specific genes have been shown to be essential for their expression, it is unclear which NFI gene products function in specific tissues during development. We have isolated cDNAs from all four murine NFI genes (gene designations Nfia, Nfib, Nfic, and Nfix), assessed the embryonic and postnatal expression patterns of the NFI genes, and determined the ability of specific NFI proteins to activate transcription from the NFI-dependent mouse mammary tumor virus (MMTV) promoter. In adult mice, all four NFI genes are most highly expressed in lung, liver, heart, and other tissues but only weakly expressed in spleen and testis. The embryonic expression patterns of the NFI genes is complex, with NFI-A transcripts appearing earliest-within 9 days postcoitum in the heart and developing brain. The four genes exhibit unique but overlapping patterns of expression during embryonic development, with high level expression of NFI-A, NFI-B, and NFI-X transcripts in neocortex and extensive expression of the four genes in muscle, connective tissue, liver, and other organ systems. The four NFI gene products studied differ in their ability to activate expression of the NFI-dependent MMTV promoter, with the NFI-B protein being most active and the NFI-A protein being least active. These data are discussed in the context of the developmental expression patterns of known NFI-responsive genes. The differential activation of an NFI-dependent promoter, together with the expression patterns observed for the four genes, indicate that the NFI proteins may play an important role in regulating tissue-specific gene expression during mammalian embryogenesis.

Antistaphylococcal activities of sparfloxacin (CI-978; AT-4140), ofloxacin, and ciprofloxacin

The activity of sparfloxacin (CI-978; AT-4140) was compared with those of ofloxacin and ciprofloxacin against clinical isolates of Staphylococcus aureus and Staphylococcus epidermidis. All 10 ciprofloxacin-resistant staphylococci had reduced susceptibility to sparfloxacin and ofloxacin. Against 105 ciprofloxacin-susceptible strains of S. aureus, the sparfloxacin MIC for 90% of strains tested was at least fourfold lower than those of ciprofloxacin and ofloxacin, while against 104 ciprofloxacin-susceptible strains of S. epidermidis, the MIC of sparfloxacin for 90% of strains tested was twofold lower than that of ciprofloxacin and fourfold lower than that of ofloxacin. MBCs of sparfloxacin were less than or equal to 4 x MICs. The effects of inoculum size and pH variations, as well as the presence of serum, on the MICs of sparfloxacin were minimal. Subinhibitory concentrations of sparfloxacin did reduce adherence of S. epidermidis.

Cutaneous manifestations of intestinal helminthic infections

Several intestinal helminths may involve the skin. In cutaneous larva migrans and enterobiasis this is often the only organ involved, whereas hookworm and trichinosis are characterized by multisystem disease. The clinical spectrum of strongyloidiasis may range from a low-grade chronic dermatitis to a fulminant, often fatal, hyperinfection syndrome in the immunocompromised host. In the absence of recent breakthroughs in diagnostic testing, a meticulous history and knowledge of the life cycles and the often characteristic skin manifestations of these parasites remain essential to prompt diagnosis and effective treatment.