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On the optimal feedback control of linear quantum systems in the presence of thermal noise

We study the possibility of taking bosonic systems subject to quadratic Hamiltonians and a noisy thermal environment to non-classical stationary states by feedback loops based on weak measurements and conditioned linear driving. We derive general analytical upper bounds for the single mode squeezing and multimode entanglement at steady state, depending only on the Hamiltonian parameters and on the number of thermal excitations of the bath. Our findings show that, rather surprisingly, larger number of thermal excitations in the bath allow for larger steady-state squeezing and entanglement if the efficiency of the optimal continuous measurements conditioning the feedback loop is high enough. We also consider the performance of feedback strategies based on homodyne detection and show that, at variance with the optimal measurements, it degrades with increasing temperature.Comment: 10 pages, 2 figures. v2: minor changes to the letter; better explanation of the necessary and sufficient conditions to achieve the bounds (in the supplemental material); v3: title changed; comparison between optimal general-dyne strategy and homodyne strategy is discussed; supplemental material included in the manuscript and few references added. v4: published versio

Incidence and pathophysiology of atrioventricular block following mitral valve replacement and ring annuloplasty

Background: In this retrospective study we evaluate the causative mechanisms underlying postoperative atrioventricular block (AVB) following mitral valve replacement and mitral valve annuloplasty. Methods: Between January 1990 and December 2003, 391 patients underwent mitral valve replacement or ring annuloplasty and quadrangular resection. Exclusion criteria were preoperative AV block, two or three valvular procedures, reoperations and procedures combined with coronary artery bypass grafting. The presence of the postoperative AVB was compared with preoperative and intraoperative variables. On 55 post-mortem specimens the relationship between the AV node, AV node artery and mitral valve annulus was investigated. Results: The mean age was 59±14 years and 44% of patients were female. Postoperatively AVB occurred in 92 (23.5%) patients. AVB III was found in 17 (4%) patents, in whom a pacemaker was implanted within median interval of 4 days. Second degree AVB occurred and first degree AVB in five (1.3%) and in 70 (18%) patients respectively. In dry dissected human hearts in 23% of investigated cases the AV node artery was discovered to run close to the annulus of the mitral valve. Conclusions: Data collected in this study showed that, sotalol and amiodarone as well as a prolonged cross-clamp time may slightly influence the 23% incidence of postoperative AVB. The morphological investigation showed that the AV node artery runs in close proximity to the annulus in 23% of cases. We speculate that damage of the AV node artery may play a role in development of AV

Optimal estimation of joint parameters in phase space

We address the joint estimation of the two defining parameters of a displacement operation in phase space. In a measurement scheme based on a Gaussian probe field and two homodyne detectors, it is shown that both conjugated parameters can be measured below the standard quantum limit when the probe field is entangled. We derive the most informative Cram\'er-Rao bound, providing the theoretical benchmark on the estimation and observe that our scheme is nearly optimal for a wide parameter range characterizing the probe field. We discuss the role of the entanglement as well as the relation between our measurement strategy and the generalized uncertainty relations.Comment: 8 pages, 3 figures; v2: references added and sections added to the supplemental material; v3: minor changes (published version

Summing Planar Diagrams by an Integrable Bootstrap

Correlation functions of matrix-valued fields are not generally known for massive renormalized field theories. We find the large-N limit of form factors of the (1+1)-dimensional sigma model with SU(N) X SU(N) symmetry. These form factors give a correction to the free-field approximation for the N=infinity Wightman function. The method is a combination of the 1/N-expansion of the S-matrix and Smirnov's form-factor axioms. We expand the renormalized field in terms of a free massive Bosonic field as N goes to infinity.Comment: 10 pages, revtex. Fixing of further misprints. Version to appear in Phys. Rev.

Photography as an act of collaboration

The camera is usually considered to be a passive tool under the control of the operator. This definition implicitly constrains how we use the medium, as well as how we look at – and what we see in – its interpretations of scenes, objects, events and ‘moments’. This text will suggest another way of thinking about – and using – the photographic medium. Based on the evidence of photographic practice (mine and others’), I will suggest that, as a result of the ways in which the medium interprets, juxtaposes and renders the elements in front of the lens, the camera is capable of depicting scenes, events and moments that did not exist and could not have existed until brought into being by the act of photographing them. Accordingly, I will propose that the affective power of many photographs is inseparable from their ‘photographicness’ – and that the photographic medium should therefore be considered as an active collaborator in the creation of uniquely photographic images

Detection of Torquetenovirus and Redondovirus DNA in Saliva Samples from SARS-CoV-2-Positive and -Negative Subjects

Torquetenovirus (TTV) and Redondovirus (ReDoV) are the most prevalent viruses found in the human respiratory virome in viral metagenomics studies. A large-scale epidemiological study was performed to investigate their prevalence and loads in saliva samples according to SARS-CoV-2 status

Safe, effective and durable epicardial left atrial appendage clip occlusion in patients with atrial fibrillation undergoing cardiac surgery: first long-term results from a prospective device trial

OBJECTIVES Atrial fibrillation (AF) is a significant risk factor for embolic stroke originating from the left atrial appendage (LAA). This is the first report of long-term safety and efficacy data on LAA closure using a novel epicardial LAA clip device in patients undergoing cardiac surgery. METHODS Forty patients with AF were enrolled in this prospective ‘first-in-man' trial. The inclusion criterion was elective cardiac surgery in adult patients with AF for which a concomitant ablation procedure was planned. Intraoperative transoesophageal echocardiography (TEE) was used to exclude LAA thrombus at baseline and evaluate LAA perfusion after the procedure, while computed tomography (CT) was used for serial imagery workup at baseline, 3-, 12-, 24- and 36-month follow-up. RESULTS Early mortality was 10% due to non-device-related reasons, and thus 36 patients were included in the follow-up consisting of 1285 patient-days and mean duration of 3.5 ± 0.5 years. On CT, clips were found to be stable, showing no secondary dislocation 36 months after surgery. No intracardial thrombi were seen, none of the LAA was reperfused and in regard to LAA stump, none of the patients demonstrated a residual neck >1 cm. Apart from one unrelated transient ischaemic attack (TIA) that occurred 2 years after surgery in a patient with carotid plaque, no other strokes and/or neurological events demonstrated in any of the studied patients during follow-up. CONCLUSION This is the first prospective trial in which concomitant epicardial LAA occlusion using this novel epicardial LAA clip device is 100% effective, safe and durable in the long term. Closure of the LAA by epicardial clipping is applicable to all-comers regardless of LAA morphology. Minimal access epicardial LAA clip closure may become an interesting therapeutic option for patients in AF who are not amenable to anticoagulation and/or catheter closure. Further data are necessary to establish LAA occlusion as a true and viable therapy for stroke prevention. CLINICAL TRIAL REGISTRATION The trial is registered at www.ClinicalTrials.gov, reference: NCT0056751