Variational ansatz-based quantum simulation of imaginary time evolution

Imaginary time evolution is a powerful tool for studying quantum systems. While it is possible to simulate with a classical computer, the time and memory requirements generally scale exponentially with the system size. Conversely, quantum computers can efficiently simulate quantum systems, but not non-unitary imaginary time evolution. We propose a variational algorithm for simulating imaginary time evolution on a hybrid quantum computer. We use this algorithm to find the ground-state energy of many-particle systems; specifically molecular hydrogen and lithium hydride, finding the ground state with high probability. Our method can also be applied to general optimisation problems and quantum machine learning. As our algorithm is hybrid, suitable for error mitigation and can exploit shallow quantum circuits, it can be implemented with current quantum computers.Comment: 14 page

Error-mitigated digital quantum simulation

Variational algorithms may enable classically intractable simulations on near-future quantum computers. However, their potential is limited by hardware errors. It is therefore crucial to develop efficient ways to mitigate these errors. Here, we propose a stabiliser-like method which enables the detection of up to 60 - 80 % of depolarising errors. Our method is suitable for near-term quantum hardware. Simulations show that our method can significantly benefit calculations subject to both stochastic and correlated noise, especially when combined with existing error mitigation techniques.Comment: Published versio

Virtual Distillation for Quantum Error Mitigation

Contemporary quantum computers have relatively high levels of noise, making it difficult to use them to perform useful calculations, even with a large number of qubits. Quantum error correction is expected to eventually enable fault-tolerant quantum computation at large scales, but until then it will be necessary to use alternative strategies to mitigate the impact of errors. We propose a near-term friendly strategy to mitigate errors by entangling and measuring $M$ copies of a noisy state $\rho$. This enables us to estimate expectation values with respect to a state with dramatically reduced error, $\rho^M/ \mathrm{Tr}(\rho^M)$, without explicitly preparing it, hence the name "virtual distillation". As $M$ increases, this state approaches the closest pure state to $\rho$, exponentially quickly. We analyze the effectiveness of virtual distillation and find that it is governed in many regimes by the behavior of this pure state (corresponding to the dominant eigenvector of $\rho$). We numerically demonstrate that virtual distillation is capable of suppressing errors by multiple orders of magnitude and explain how this effect is enhanced as the system size grows. Finally, we show that this technique can improve the convergence of randomized quantum algorithms, even in the absence of device noise

Is there a hormonal regulation of phagocytosis at unicellular and multicellular levels? A critical review

Phagocytosis is an ancient cell function, which is similar at unicellular and multicellular levels. Unicells synthesize, store, and secrete multicellular (mammalian) hormones, which influence their phagocytosis. Amino acid hormones, such as histamine, serotonin, epinephrine, and melatonin stimulate phagocytosis, whereas peptide hormones, such as adrenocorticotropic hormone (ACTH), insulin, opioids, arginine vasopressin, and atrial natriuretic peptide decreased it, independently on their chemical structure or function in multicellulars. Macrophage phagocytosis of multicellulars is also stimulated by amino acid hormones, such as histamine, epinephrine, melatonin, and thyroid hormones, however, the effect of peptide hormones is not uniform: prolactin, insulin, glucagon, somatostatin, and leptin have positive effects, whereas ACTH, human chorionic gonadotropin, opioids, and ghrelin have negative ones. Steroid hormones, such as estrogen, hydrocortisone, and dexamethasone are stimulating macrophage phagocytosis, whereas progesterone, aldosterone, and testosterone are depressing it. Considering the data and observations there is not a specific phagocytosis hormone, or a hormonal regulation of phagocytosis neither unicellular, nor multicellular level, however, hormones having specific functions in multicellulars also influence phagocytosis at both levels universally (in unicellulars) or individually (in macrophages). Nevertheless, the hormonal influence cannot be neglected, as phagocytosis (as a function) is rather sensitive to minute dose of hormones and endocrine disruptors. The hormonal influence of phagocytosis by macrophages can be deduced to the events at unicellular level

OpenFermion: The Electronic Structure Package for Quantum Computers

Quantum simulation of chemistry and materials is predicted to be an important application for both near-term and fault-tolerant quantum devices. However, at present, developing and studying algorithms for these problems can be difficult due to the prohibitive amount of domain knowledge required in both the area of chemistry and quantum algorithms. To help bridge this gap and open the field to more researchers, we have developed the OpenFermion software package (www.openfermion.org). OpenFermion is an open-source software library written largely in Python under an Apache 2.0 license, aimed at enabling the simulation of fermionic models and quantum chemistry problems on quantum hardware. Beginning with an interface to common electronic structure packages, it simplifies the translation between a molecular specification and a quantum circuit for solving or studying the electronic structure problem on a quantum computer, minimizing the amount of domain expertise required to enter the field. The package is designed to be extensible and robust, maintaining high software standards in documentation and testing. This release paper outlines the key motivations behind design choices in OpenFermion and discusses some basic OpenFermion functionality which we believe will aid the community in the development of better quantum algorithms and tools for this exciting area of research.Comment: 22 page

Compliance with Positive Airway Pressure Treatment for Obstructive Sleep Apnea

ObjectivesPositive airway pressure (PAP) is considered a standard treatment for moderate-to-severe obstructive sleep apnea (OSA) patients. However, compliance with PAP treatment is suboptimal because of several types of discomfort experienced by patients. This study investigated compliance with PAP therapy, and affecting factors for such compliance, in OSA patients.MethodsWe performed a survey on 69 patients who engaged in PAP therapy between December 2006 and November 2007. After diagnostic polysomnography and manual titration, patients trialed PAP using the ResMed instrument and explored autoadjusting PAP (APAP), continuous PAP (CPAP), and flexible PAP (using expiratory pressure relief [EPR]) at least once every week for 1 month. Compliance measures were mean daily use (hr), percentage of days on which PAP was used, and percentage of days on which PAP was used for >4 hr. Data were obtained at night using the software Autoscan version 5.7® of the ResMed Inc. We obtained data on anthropometric (age, BMI, neck circumflex, Epworth sleepiness scale, Pittsburgh Sleep Quality Index, hypertension, alcohol intake), polysomnographic data (severity of apnea-hypopnea index [AHI], proportion of nonsupine sleep time, position dependence of sleep), PAP mode and AHI during PAP use for affecting factors.ResultsAfter 1 month, 41 of the 69 patients (59.4%) were pleased with PAP therapy and purchased instruments. Twenty-four patients (34.7%) used PAP for more than 3 months. The percentage of days on which PAP was used was statistically higher in patients with hypertension than in normotensive patients (P=0.003). There were negative correlations 1) between nonsupine position sleep time and percentage of days on which PAP was used (r=-0.424, P=0.039), and 2) between the AHI during PAP use and the percentage of days on which PAP was used for >4 hr (r=-0.443, P=0.030). There were no statistical differences between AHI, BMI, PAP pressure, or other measured parameters, on the one hand, and compliance, on the other.ConclusionThe affecting factors for PAP use were hypertension history, sleep posture (shorter nonsupine sleep time), and lower AHI during PAP use

Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial

Background Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy