Nonclassical photon pairs from warm atomic vapor using a single driving laser.

Generation of nonclassical light is an essential tool for quantum optics research and applications in quantum information technology. We present realization of the source of nonclassically correlated photon pairs based on the process of spontaneous four-wave-mixing in warm atomic vapor. Atoms are excited only by a single laser beam in retro-reflected configuration and narrowband frequency filtering is employed for selection of correlated photon pairs. Nonclassicality of generated light fields is proved by analysis of their statistical properties. Measured parameters of the presented source promise further applicability for efficient interaction with atomic ensembles.

Risk comparison of bleeding and ischemic perioperative complications after acute and elective orthopedic surgery in patients with cardiovascular disease.

INTRODUCTION: The study objective was to ascertain the incidence of bleeding and ischemic complications related to acute and planned orthopedic surgery in patients with known cardiovascular diseases. MATERIALS AND METHODS: The study conducted between 2010 and 2013 enrolled 477 patients (289 women, 188 men) with a diagnosed cardiovascular disease or a history of thromboembolic event. Aside from gender, age, height and weight, the study observed other anamnestic data and perioperative laboratory test results that may impact on a bleeding or ischemic event. RESULTS: Two hundred seventy-two (57 %) patients had acute surgery, and 205 (43 %) patients had elective surgery. Complications arose in 55 (11.6 %) patients, 32 (6.9 %) had bleeding complications, 19 (4.0 %) ischemic complications, and both complications were experienced by 4 (0.8 %) patients. Bleeding developed in 14 (5.1 %) patients who had acute surgery, and in 22 (10.7 %) who had elective surgery. Twenty-two (8.1 %) patients having acute surgery and one (0.1 %) undergoing elective surgery suffered from ischemic complications. The incidence of bleeding complications was significantly higher in elective surgery (p = 0.026, OR 2.22), and when adjusted (general anaesthesia, gender, and use of warfarin), the difference was even higher (p = 0.015, OR 2.44), whereas the occurrence of ischemic complications was significantly higher in acute surgery (p = 0.005, OR 18.0), and when adjusted (age), the difference remained significant (p = 0.044, OR 8.3). CONCLUSIONS: The study noted a significantly higher incidence of bleeding complications in elective orthopedic surgery when compared with acute surgery. Conversely, the incidence of ischemic complications was significantly higher in patients having acute orthopedic surgery when compared with those operated on electively.

[Surgical Correction of Scoliosis: Does Intraoperative CT Navigation Prolong Operative Time?] / Operacní korekce skoliózy: prodluzuje peroperacní CT navigace trvání operace?

PURPOSE OF THE STUDY The aim of the study was to compare the duration of corrective surgery for scoliosis in relation to the intra-operative use of either fluoroscopic or CT navigation. MATERIAL AND METHODS The indication for surgery was adolescent idiopathic scoliosis in younger patients and degenerative scoliosis in middleage or elderly patients. In a retrospective study, treatment outcomes in 43 consecutive patients operated on between April 2011 and April 2014 were compared. Only patients undergoing surgical correction of five or more spinal segments (fixation of six and more vertebrae) were included. RESULTS Transpedicular screw fixation of six to 13 vertebrae was performed under C-arm fluoroscopy guidance in 22 patients, and transpedicular screws were inserted in six to 14 vertebrae using the O-arm imaging system in 21 patients. A total of 246 screws were placed using the C-arm system and 340 screws were inserted using the O-arm system (p < 0.001). The procedures with use of the O-arm system were more complicated and required an average operative time longer by 48% (measured from the first skin incision to the completion of skin suture). However, the mean time needed for one screw placement (the sum of all surgical procedures with the use of a navigation technique divided by the number of screws placed using this technique) was the same in both techniques (19 min). DISCUSSION With good teamwork (surgeons, anaesthesiologists and a radiologist attending to the O-arm system), the time required to obtain one intra-operative CT scan is 3 to 5 minutes. The study showed that the mean time for placement of one screw was identical in both techniques although the average operative time was longer in surgery with O-arm navigation. The 19- minute interval was not the real placement time per screw. It was the sum of all operative times of surgical procedures (from first incision to suture completion including the whole approach within the range of planned stabilization) which used the same navigation technique divided by the number of all screws inserted during the procedures. The longer average operative time in procedures using O-arm navigation was not related to taking intra-operative O-arm scans. The authors consider surgery with an O-arm imaging system to be a safer procedure and use it currently in surgical correction of scoliosis. CONCLUSIONS The study focused on the length of surgery to correct scoliosis performed using either conventional fluoroscopy (C-arm) or intra-operative CT scanning (O-arm) showed that the mean placement time for one screw was identical in both imaging techniques when six or more vertebrae were stabilised. The use of intra-operative CT navigation did not make the surgery longer, and the higher number of inserted screws provides evidence that this technique is safer and allows us to achieve good stability of the correction procedure. Key words: virtual CT guidance, O-arm, scoliosis, transpedicular screw.

THA and TKA in patients with cardiovascular disease: What makes the risk of perioperative bleeding?

Backround: The purpose of the study was to ascertain the incidence of bleeding and ischaemic complications in patients with cardiac disease after total hip arthroplasty (THA) and total knee arthroplasty (TKA). METHODS: In total, 477 patients (289 women, 188 men) with known history of cardiac disease or thromboembolic disease treated with surgery in 2010-2013, were enrolled in the study. Perioperative prevention of thromboembolic disease using low-molecular-weight heparins was applied in all the patients. The data that could have an impact on the development of monitored perioperative complications, were observed. RESULTS: Complications occurred in 55 (11.6 %) patients: bleeding complications in 32, ischaemic in 19, and both in four patients. Complications were found in 13 (12.0 %) patients after THA and in 6 (9.5 %) patients after TKA. Bleeding complications were observed in 17 patients after THA and TKA, ischaemic in one, and both simultaneously in one patient.Bleeding complications occurred insignificantly more frequently after THA and TKA (p = 0.094); however, this difference was statistically significant after adjustment for risk factors (p = 0.003). On the contrary, ischaemic complications were significantly more frequent after other skeletal surgeries (p = 0.014). Nevertheless, this difference was not statistically significant after the adjustment (p = 0.880). The comparison of the risk of complications in patients after THA with that in patients after TKA showed no significant difference (p = 0.580). CONCLUSION: The study showed a significantly higher incidence of bleeding complications in patients after THA and TKA compared to other surgeries of the musculoskeletal system in patients with a history of cardiac disease. Bleeding complications cannot be detected in advance (Tab. 1, Ref. 16).

[Risk of death in patients with unstable pelvic fracture and large vessel injury]. / Riziko úmrtí pacienta s nestabilní zlomeninou pánve a poranením velkých cév.

INTRODUCTION: The aim of the study was to provide accurate data regarding the incidence of large vessel injury as part of pelvic trauma in patients treated during a 12-year period. METHODS: In total, 715 patients admitted and treated for pelvic fractures from 2001-2012 were analyzed. Data on large vessel injuries (aorta, inferior vena cava, common iliac artery and vein) reported in perioperative or autopsy findings were obtained from the patient database. The statistical significance of achieved results was tested using contingency tables (chi-square test of independence or Fisher factorial test). The significance level for the calculated tests was chosen to be 5%. RESULTS: Sixty six (9%) patients died in the first hours after admission, 43 (6%) of them prior to surgery. Seventy (10%) underwent urgent surgeries, 47 (7%) of whom survived and 23 (3%) died. A large vessel injury in the pelvic region was detected in 13 (2%) patients. In the surviving surgical patients, a serious injury of pelvic venous plexus, as the only source of bleeding, was found only once (2%), while in patients who deceased post-surgically and pre-surgically, serious vascular injury in the pelvic region was diagnosed in 5 and 7 patients in both subgroups (22% and 41%, resp.). This difference was significantly higher in comparison with surviving patients (p=0.0002 and p=0.0109, resp.). CONCLUSION: The incidence of large vessel injury with severe bleeding associated with pelvic trauma was low in our study; however, the risk of death in patients with this injury was significantly higher. The results of our study support the hypothesis that in most patients a large artery or vein injury in combination with massive bleeding from the venous plexus due to a dislocated pelvic fracture results in death even before arrival of emergency services. This hypothesis could be verified in a study including also autopsy findings in persons who died even before hospital admission. KEY WORDS: unstable pelvic injury vascular injury risk of death.

Efficient experimental estimation of fidelity of linear optical quantum Toffoli gate.

We propose an efficiently measurable lower bound on quantum process fidelity of N-qubit controlled-Z gates. This bound is determined by average output state fidelities for N partially conjugate product bases. A distinct advantage of our approach is that only fidelities with product states need to be measured while keeping the total number of measurements much smaller than what is necessary for full quantum process tomography. As an application, we use this method to experimentally estimate quantum process fidelity F of a three-qubit linear optical quantum Toffoli gate and we find that F≥0.83. We also demonstrate the entangling capability of the gate by preparing Greenberger-Horne-Zeilinger-type three-qubit entangled states from input product states.

Noiseless loss suppression in quantum optical communication.

We propose a protocol for conditional suppression of losses in direct quantum state transmission over a lossy quantum channel. The method works by noiselessly attenuating the input state prior to transmission through a lossy channel followed by noiseless amplification of the output state. The procedure does not add any noise; hence, it keeps quantum coherence. We experimentally demonstrate it in the subspace spanned by vacuum and single-photon states, and consider its general applicability.

[The influence of patient age and mechanism of injury on the type of pelvic fracture: epidemiological study]. / Vliv veku pacienta a mechanismu úrazu na typ zlomeniny pánve: epidemiologická studie.

PURPOSE OF THE STUDY: The patients with pelvic ring injury involve two groups: 1) young and middle-age persons, mostly men, with serious injury to the pelvic ring due to high-energy trauma; and 2) older patients, mostly women, with osteoporotic fractures due to a simple fall. The aim of this study was to show significant differences in the selected epidemiological characteristics between these two groups. MATERIAL AND METHODS: The group comprised 225 patients older than 15 years with pelvic fractures who were treated between January 1, 2007, and December 31, 2009. In this retrospective descriptive study, the patients' data on age, gender, mechanism of injury and a type of fracture according to the AO classification were retrieved and analysed. Categorical data at a level of significance of 5% were compared using the Chi-square test. RESULTS: In the group reviewed there were 113 women and 112 men, with an average age of 51 years (women, 53 years; men, 49 years) in the range of 15 to 95 years. More men than women were in the age range of 15 to 60 years (with the difference being significant only in the sixth decade of life; p=0.043). In the age category of over sixty, women outnumbered men, and this was significant in the eight and ninth decades (p=0.023 and p=0.04, respectively). Significantly more men were involved in motorbike accidents (p=0.047) or had falls from heights (p=0.004) and particularly those at a worksite (p<0.001). Fractures due to a simple fall were significantly more frequent in women than men (p<0.001) and, generally, were most often found in the old-age category, in which women were eight years senior to men. Type A fractures were found in 58, type B fractures in 140 and type C fractures in 27 patients. The most frequent fractures (A2.2, p=0.054; B2.1, p=0.038) occurred more often in women and at a much higher age than in men (the age difference was 15 years in type A2.2 fractures and "only" 7 years in type B2.1 fractures). The patients who sustained either of these fractures in a simple fall were about 35 years older than those in whom these fractures were caused by high-energy trauma. DISCUSSION: The fact that pelvic injuries most often occur in men at young or middle age has been confirmed by several epidemiological studies with a conclusion that age-related risky male behaviours play a significant role. The findings of this study showed that pelvic fractures due to simple falls were mostly found in old-age patients, with women eight years older than men. This provides evidence for the existence of two distinct groups of patients with pelvic fractures. The existence of two epidemiologically different groups of patients with pelvic fractures, in the authors' opinion, is demonstrated by a correlation of AO fracture type, patient gender and age in each group. A mere comparison of the age of patients indicates that older patients had mostly type A and B fractures. Unilateral fractures of the pubic ramus after a simple fall, which are regarded as related to osteoporosis, were recorded in a significantly higher number of women of the oldest age. The authors suggest that epidemiological studies of pelvic injuries should use the age of 70+ as an exclusion criterion in the patients with type A2.2 and B2.1 fractures. This will remove the bias of epidemiological data on patients with severe pelvic injuries, resulting from involvement of patients with osteoporotic fractures. CONCLUSION: The evaluation of epidemiological data in this study allows us to conclude that younger men are those most frequently sustaining pelvic injuries due to high-energy trauma and that old age (80+) is characteristic for patients of both sexes, with female sex predominance, who have fractures due to simple falls. These findings give support to the concept that, in a group of patients with pelvic injuries, a subgroup with fractures different in terms of epidemiology and aetiology (osteoporotic fracture) can be identified.

Work and information from thermal states after subtraction of energy quanta.

Quantum oscillators prepared out of thermal equilibrium can be used to produce work and transmit information. By intensive cooling of a single oscillator, its thermal energy deterministically dissipates to a colder environment, and the oscillator substantially reduces its entropy. This out-of-equilibrium state allows us to obtain work and to carry information. Here, we propose and experimentally demonstrate an advanced approach, conditionally preparing more efficient out-of-equilibrium states only by a weak dissipation, an inefficient quantum measurement of the dissipated thermal energy, and subsequent triggering of that states. Although it conditionally subtracts the energy quanta from the oscillator, average energy grows, and second-order correlation function approaches unity as by coherent external driving. On the other hand, the Fano factor remains constant and the entropy of the subtracted state increases, which raise doubts about a possible application of this approach. To resolve it, we predict and experimentally verify that both available work and transmitted information can be conditionally higher in this case than by arbitrary cooling or adequate thermal heating up to the same average energy. It qualifies the conditional procedure as a useful source for experiments in quantum information and thermodynamics.

Experimental demonstration of a fully inseparable quantum state with nonlocalizable entanglement.

Localizability of entanglement in fully inseparable states is a key ingredient of assisted quantum information protocols as well as measurement-based models of quantum computing. We investigate the existence of fully inseparable states with nonlocalizable entanglement, that is, with entanglement which cannot be localized between any pair of subsystems by any measurement on the remaining part of the system. It is shown, that the nonlocalizable entanglement occurs already in suitable mixtures of a three-qubit GHZ state and white noise. Further, we generalize this set of states to a two-parametric family of fully inseparable three-qubit states with nonlocalizable entanglement. Finally, we demonstrate experimentally the existence of nonlocalizable entanglement by preparing and characterizing one state from the family using correlated single photons and linear optical circuit.

Experimental investigation of a four-qubit linear-optical quantum logic circuit.

We experimentally demonstrate and characterize a four-qubit linear-optical quantum logic circuit. Our robust and versatile scheme exploits encoding of two qubits into polarization and path degrees of single photons and involves two crossed inherently stable interferometers. This approach allows us to design a complex quantum logic circuit that combines a genuine four-qubit C(3)Z gate and several two-qubit and single-qubit gates. The C(3)Z gate introduces a sign flip if and only if all four qubits are in the computational state |1〉. We verify high-fidelity performance of this central four-qubit gate using Hofmann bounds on quantum gate fidelity and Monte Carlo fidelity sampling. We also experimentally demonstrate that the quantum logic circuit can generate genuine multipartite entanglement and we certify the entanglement with the use of suitably tailored entanglement witnesses.

Faithful conditional quantum state transfer between weakly coupled qubits.

One of the strengths of quantum information theory is that it can treat quantum states without referring to their particular physical representation. In principle, quantum states can be therefore fully swapped between various quantum systems by their mutual interaction and this quantum state transfer is crucial for many quantum communication and information processing tasks. In practice, however, the achievable interaction time and strength are often limited by decoherence. Here we propose and experimentally demonstrate a procedure for faithful quantum state transfer between two weakly interacting qubits. Our scheme enables a probabilistic yet perfect unidirectional transfer of an arbitrary unknown state of a source qubit onto a target qubit prepared initially in a known state. The transfer is achieved by a combination of a suitable measurement of the source qubit and quantum filtering on the target qubit depending on the outcome of measurement on the source qubit. We experimentally verify feasibility and robustness of the transfer using a linear optical setup with qubits encoded into polarization states of single photons.