Clock Quantum Monte Carlo: an imaginary-time method for real-time quantum dynamics

In quantum information theory, there is an explicit mapping between general unitary dynamics and Hermitian ground state eigenvalue problems known as the Feynman-Kitaev Clock. A prominent family of methods for the study of quantum ground states are quantum Monte Carlo methods, and recently the full configuration interaction quantum Monte Carlo (FCIQMC) method has demonstrated great promise for practical systems. We combine the Feynman-Kitaev Clock with FCIQMC to formulate a new technique for the study of quantum dynamics problems. Numerical examples using quantum circuits are provided as well as a technique to further mitigate the sign problem through time-dependent basis rotations. Moreover, this method allows one to combine the parallelism of Monte Carlo techniques with the locality of time to yield an effective parallel-in-time simulation technique

Boson Sampling for Molecular Vibronic Spectra

Quantum computers are expected to be more efficient in performing certain computations than any classical machine. Unfortunately, the technological challenges associated with building a full-scale quantum computer have not yet allowed the experimental verification of such an expectation. Recently, boson sampling has emerged as a problem that is suspected to be intractable on any classical computer, but efficiently implementable with a linear quantum optical setup. Therefore, boson sampling may offer an experimentally realizable challenge to the Extended Church-Turing thesis and this remarkable possibility motivated much of the interest around boson sampling, at least in relation to complexity-theoretic questions. In this work, we show that the successful development of a boson sampling apparatus would not only answer such inquiries, but also yield a practical tool for difficult molecular computations. Specifically, we show that a boson sampling device with a modified input state can be used to generate molecular vibronic spectra, including complicated effects such as Duschinsky rotations.Comment: 10 pages, 6 figure

Increasing the representation accuracy of quantum simulations of chemistry without extra quantum resources

Proposals for near-term experiments in quantum chemistry on quantum computers leverage the ability to target a subset of degrees of freedom containing the essential quantum behavior, sometimes called the active space. This approximation allows one to treat more difficult problems using fewer qubits and lower gate depths than would otherwise be possible. However, while this approximation captures many important qualitative features, it may leave the results wanting in terms of absolute accuracy (basis error) of the representation. In traditional approaches, increasing this accuracy requires increasing the number of qubits and an appropriate increase in circuit depth as well. Here we introduce a technique requiring no additional qubits or circuit depth that is able to remove much of this approximation in favor of additional measurements. The technique is constructed and analyzed theoretically, and some numerical proof of concept calculations are shown. As an example, we show how to achieve the accuracy of a 20 qubit representation using only 4 qubits and a modest number of additional measurements for a simple hydrogen molecule. We close with an outlook on the impact this technique may have on both near-term and fault-tolerant quantum simulations

Urinary naphthalene and phenanthrene as biomarkers of occupational exposure to polycyclic aromatic hydrocarbons.

OBJECTIVES: The study investigated the utility of unmetabolised naphthalene (Nap) and phenanthrene (Phe) in urine as surrogates for exposures to mixtures of polycyclic aromatic hydrocarbons (PAHs). METHODS: The report included workers exposed to diesel exhausts (low PAH exposure level, n = 39) as well as those exposed to emissions from asphalt (medium PAH exposure level, n = 26) and coke ovens (high PAH exposure level, n = 28). Levels of Nap and Phe were measured in urine from each subject using head space-solid phase microextraction and gas chromatography-mass spectrometry. Published levels of airborne Nap, Phe and other PAHs in the coke-producing and aluminium industries were also investigated. RESULTS: In post-shift urine, the highest estimated geometric mean concentrations of Nap and Phe were observed in coke-oven workers (Nap: 2490 ng/l; Phe: 975 ng/l), followed by asphalt workers (Nap: 71.5 ng/l; Phe: 54.3 ng/l), and by diesel-exposed workers (Nap: 17.7 ng/l; Phe: 3.60 ng/l). After subtracting logged background levels of Nap and Phe from the logged post-shift levels of these PAHs in urine, the resulting values (referred to as ln(adjNap) and ln(adjPhe), respectively) were significantly correlated in each group of workers (0.71 < or = Pearson r < or = 0.89), suggesting a common exposure source in each case. Surprisingly, multiple linear regression analysis of ln(adjNap) on ln(adjPhe) showed no significant effect of the source of exposure (coke ovens, asphalt and diesel exhaust) and further suggested that the ratio of urinary Nap/Phe (in natural scale) decreased with increasing exposure levels. These results were corroborated with published data for airborne Nap and Phe in the coke-producing and aluminium industries. The published air measurements also indicated that Nap and Phe levels were proportional to the levels of all combined PAHs in those industries. CONCLUSION: Levels of Nap and Phe in urine reflect airborne exposures to these compounds and are promising surrogates for occupational exposures to PAH mixtures

UK National Audit of Early Syphilis Management. Clinics audit: screening for and management of early syphilis

Data were provided by 131 clinics, and 56% of cases were managed in clinics in the London regions in 2003. Three clinics (2%) do not routinely screen new patients for syphilis, and 28 clinics (21%) do not routinely screen ‘rebook’ patients who have had a new partner. More than 80% of clinics routinely conduct cardiovascular and neurological examinations, although chest radiography is only performed by 50% of clinics and lumbar puncture by 13%. Only 19 (14%) clinics indicated not routinely using the recommended procaine penicillin G (PPG) regimen or one- or two-dose benzathine penicillin G (BPG) regimens for early syphilis, with 57% providing two doses of BPG 2.4 g, 40% providing PPG 750 mg for 10 days, and 15% providing one dose of BPG 2.4 g. Only seven clinics (5%) indicated that they provided treatment for early syphilis with PPG that is inferior to that recommended in the national guidelines. Only 18 clinics specified using the recommended dose and duration (or in excess of this) of PPG for neurosyphilis for cases with HIV infection. Provision for management of severe penicillin reaction is good, although few patients are desensitized. All clinics report that contact tracing for early syphilis is provided, and is mainly the responsibility of health advisers. Compared with auditing outcomes, audit of management policies overestimated performance in contact tracing and provision of dark ground microscopy

UK National Audit of Early Syphilis Management. Case notes audit: diagnosis and treatment

A national audit of 781 early syphilis cases presenting during 2002–03 in UK genitourinary medicine clinics was conducted in late 2004, organized through the Regional Audit Groups. Data were aggregated by region and National Health Service trust, allowing practice to be compared between regions, between trusts within regions, as well as to national averages and the UK National Guidelines. An enzyme immunoassay was used to diagnose 695 (89%) cases (regional range 18–100%). Use of a non-treponemal test was not recorded for 44 (6%) cases. Dark ground microscopy was used in the diagnosis of only 80 (29%) primary cases. Uptake of HIV testing was 77% (range 69–94%). Nationally, 527 (67%) treatments were parenteral, with almost equal use of benzathine penicillin G for 262 (50%, range 0–97%) cases and procaine penicillin G (PPG) for 260 cases (49%, range 3–100%). There were 14 (5%) treatments with less than the recommended 750 mg dose of PPG. One hundred and five (40%) PPG treatments were with greater than 750 mg and/or for longer than 10 days of which 76 (72%) were for early latent syphilis and/or cases with HIV infection. One hundred and ninety two (86%, range 0–100%) of all oral treatments were with doxycycline. The recommended regimen of 100 mg doxycycline twice daily for 14 days was used for 104 (53%) cases; the other 91 (47%) treatments were with a variety of regimens, mainly treatments with larger doses and/or longer treatment intervals and some combination treatments. Fourteen (2%) cases were not treated; treatment was not reported for seven (0.9%) and not known for 10 (1.3%) cases, who were treated at other centres