Characterizing two-mode-squeezed light from four-wave mixing in rubidium vapor for quantum sensing and information processing.

We present a study of homodyne measurements of two-mode, vacuum-seeded, quadrature-squeezed light generated by four-wave mixing in warm rubidium vapor. Our results reveal that the vacuum squeezing can extend down to measurement frequencies of less than 1 Hz, and the squeezing bandwidth, similar to the seeded intensity-difference squeezing measured in this system, reaches up to approximately 20 MHz for typical pump parameters. By dividing the squeezing bandwidth into smaller frequency bins, we show that different sideband frequencies represent independent sources of two-mode squeezing. These properties are useful for quantum sensing and quantum information processing applications. We also investigate the impact of group velocity delays on the correlations in the system, which allows us to optimize the useful spectrum.

Veno-Arterial Extracorporeal Membrane Oxygenation for Pulmonary Embolism after Systemic Thrombolysis.

Massive pulmonary embolism (PE) is a life-threatening condition with a high mortality. Both systemic thrombolytics and veno-arterial extracorporeal membrane oxygenation (VA-ECMO) have been used in the management of massive PE. However, the safety of VA- ECMO in the setting of recent thrombolytic administration is not clear. The purpose of this study is to analyze the outcomes of patients who received VA-ECMO in the setting of systemic thrombolytics (ST). A single institution retrospective study of PE patients treated with VA-ECMO between December 2015 and December 2020 was performed. Patients who received ST were compared with those who did not receive ST. Outcomes, including mortality, major bleeding, duration of mechanical ventilation, need for renal replacement therapy, and length of hospital stay, were compared. A total of 83 patients with PE required VA-ECMO support and 18 of these received systemic thrombolytics. There was no statistically significant difference in survival to discharge between the patients who received ST compared with those who did not (88.9% vs 84.6%; p = 0.94). Major bleeding events occurred more often in patients who received ST (61.1% vs 26.2%; p = 0.01). There was no significant difference in time on mechanical ventilation, need for renal replacement therapy, or length of stay between the groups. Reasonable survival can be achieved despite an increased frequency of major bleeding events in patients that receive ST prior to VA-ECMO for PE. ST administration should not be considered an absolute contraindication to VA-ECMO. Further multi-center studies are needed to corroborate these findings.

Two-beam coupling in the production of quantum correlated images by four-wave mixing.

We investigate the effect of 2-beam coupling in different imaging geometries in generating intensity-difference squeezing from four-wave mixing (4WM) in Rb atomic vapors. A recently-introduced dual-seeding technique can cancel out the classical noise in a seeded four-wave mixing process. This dual-seeding technique, however, can introduce new complications that involve 2-beam coupling between different seeded spatial modes in the atomic vapor and can ruin squeezing at frequencies on the order of the atomic linewidth and below. This complicates some forms of quantum imaging using these systems. Here we show that seeding the 4WM process with skew rays can eliminate the excess noise caused by 2-beam coupling. To avoid 2-beam coupling in bright, seeded images, it is important to re-image the object in the gain medium, instead of focussing through it.

Catheter-based interventions versus medical and surgical approaches in acute pulmonary embolism.

OBJECTIVE: Catheter-based intervention (CBI) has become an increasingly popular option for treating pulmonary embolism (PE); however, the real benefits are unknown. The purpose of the present study was to compare the outcomes of patients treated with CBI with the outcomes of those treated with medical or surgical approaches. METHODS: We performed a retrospective analysis of patients admitted from October 2015 to December 2017 with a diagnosis of acute PE. We compared patients aged ≥18 years with a diagnosis of acute PE treated with CBI against a control group identified by propensity score matching. The control group was divided into those who had undergone surgical pulmonary embolectomy (SPE) as the surgical group and those who had not undergone SPE as the medical group. The primary outcome was mortality (in-hospital and overall mortality). The secondary outcomes were major bleeding, length of hospital stay, thrombus resolution, right ventricle improvement in systolic function and dilatation, and recurrent PE. RESULTS: Of the 108 patients, 30 were in the CBI group and 78 were in the control group (62 in the medical group and 16 in the surgical group). The patient characteristics on admission were similar, except for the body mass index, which was greater in the CBI group (P = .03). No difference was found in clinical severity, clot burden, right ventricle function, or biomarkers. Recurrent PE was less frequent in the CBI group than in the medical group (0% vs 6.4%). Otherwise, no significant differences were found in the outcomes between the CBI and medical groups. When CBI was compared with the surgical group, SPE was associated with improved mortality (0% vs 16.6%) but a longer median length of hospital stay (median, 7 days; interquartile range, 3-12 days; vs median, 8 days; interquartile range, 6.5-17 days). CONCLUSIONS: The use of CBI reduced the number of recurrent PE events compared with the medically treated patients; however, the mortality was higher than that in the surgical group.

Boarding of critically Ill patients in the emergency department.

OBJECTIVES: Emergency department boarding is the practice of caring for admitted patients in the emergency department after hospital admission, and boarding has been a growing problem in the United States. Boarding of the critically ill has achieved specific attention because of its association with poor clinical outcomes. Accordingly, the Society of Critical Care Medicine and the American College of Emergency Physicians convened a Task Force to understand the implications of emergency department boarding of the critically ill. The objective of this article is to review the U.S. literature on (1) the frequency of emergency department boarding among the critically ill, (2) the outcomes associated with critical care patient boarding, and (3) local strategies developed to mitigate the impact of emergency department critical care boarding on patient outcomes. DATA SOURCES AND STUDY SELECTION: Review article. DATA EXTRACTION AND DATA SYNTHESIS: Emergency department-based boarding of the critically ill patient is common, but no nationally representative frequency estimates has been reported. Boarding literature is limited by variation in the definitions used for boarding and variation in the facilities studied (boarding ranges from 2% to 88% of ICU admissions). Prolonged boarding in the emergency department has been associated with longer duration of mechanical ventilation, longer ICU and hospital length of stay, and higher mortality. Health systems have developed multiple mitigation strategies to address emergency department boarding of critically ill patients, including emergency department-based interventions, hospital-based interventions, and emergency department-based resuscitation care units. CONCLUSIONS: Emergency department boarding of critically ill patients was common and was associated with worse clinical outcomes. Health systems have generated a number of strategies to mitigate these effects. A definition for emergency department boarding is proposed. Future work should establish formal criteria for analysis and benchmarking of emergency department-based boarding overall, with subsequent efforts focused on developing and reporting innovative strategies that improve clinical outcomes of critically ill patients boarded in the emergency department.

Boarding of Critically Ill Patients in the Emergency Department.

OBJECTIVES: Emergency department boarding is the practice of caring for admitted patients in the emergency department after hospital admission, and boarding has been a growing problem in the United States. Boarding of the critically ill has achieved specific attention because of its association with poor clinical outcomes. Accordingly, the Society of Critical Care Medicine and the American College of Emergency Physicians convened a Task Force to understand the implications of emergency department boarding of the critically ill. The objective of this article is to review the U.S. literature on (1) the frequency of emergency department boarding among the critically ill, (2) the outcomes associated with critical care patient boarding, and (3) local strategies developed to mitigate the impact of emergency department critical care boarding on patient outcomes. DATA SOURCES AND STUDY SELECTION: Review article. DATA EXTRACTION AND DATA SYNTHESIS: Emergency department-based boarding of the critically ill patient is common, but no nationally representative frequency estimates has been reported. Boarding literature is limited by variation in the definitions used for boarding and variation in the facilities studied (boarding ranges from 2% to 88% of ICU admissions). Prolonged boarding in the emergency department has been associated with longer duration of mechanical ventilation, longer ICU and hospital length of stay, and higher mortality. Health systems have developed multiple mitigation strategies to address emergency department boarding of critically ill patients, including emergency department-based interventions, hospital-based interventions, and emergency department-based resuscitation care units. CONCLUSIONS: Emergency department boarding of critically ill patients was common and was associated with worse clinical outcomes. Health systems have generated a number of strategies to mitigate these effects. A definition for emergency department boarding is proposed. Future work should establish formal criteria for analysis and benchmarking of emergency department-based boarding overall, with subsequent efforts focused on developing and reporting innovative strategies that improve clinical outcomes of critically ill patients boarded in the emergency department.

Signal advance and delay due to an optical phase-sensitive amplifier.

Fast and slow light media exploit a steep frequency dependence in their index of refraction in order to advance or delay a modulated signal. Here we observe a qualitatively similar advance and delay from an optical phase-sensitive amplifier (PSA). Unlike in the case of slow and fast light, this effect is due to a redistribution of power between imbalanced signal sidebands, and the advance or delay is dependent on the optical phase of the input. The PSA adds energy and also changes the frequency spectrum of the input. We show that the advances and delays observed in a PSA implemented using four-wave mixing in a warm rubidium vapor are consistent with the expected behavior of an ideal PSA.

Effect of imperfect homodyne visibility on multi-spatial-mode two-mode squeezing measurements.

We study the effect of homodyne detector visibility on the measurement of quadrature squeezing for a spatially multi-mode source of two-mode squeezed light. Sources like optical parametric oscillators (OPO) typically produce squeezing in a single spatial mode because the nonlinear medium is within a mode-selective optical cavity. For such a source, imperfect interference visibility in the homodyne detector couples in additional vacuum noise, which can be accounted for by introducing an equivalent loss term. In a free-space multi-spatial-mode system imperfect homodyne detector visibility can couple in uncorrelated squeezed modes, and hence can cause faster degradation of the measured squeezing. We show experimentally the dependence of the measured squeezing level on the visibility of homodyne detectors used to probe two-mode squeezed states produced by a free space four-wave mixing process in 85Rb vapor, and also demonstrate that a simple theoretical model agrees closely with the experimental data.

Twin-beam intensity-difference squeezing below 10 Hz.

We report the generation of strong, bright-beam intensity-difference squeezing down to measurement frequencies below 10 Hz. We generate two-mode squeezing in a four-wave mixing (4WM) process in Rb vapor, where the single-pass-gain nonlinear process does not require cavity locking and only relies on passive stability. We use diode laser technology and several techniques, including dual seeding, to remove the noise introduced by seeding the 4WM process as well as the background noise. Twin-beam intensity-difference squeezing down to frequencies limited only by the mechanical and atmospheric stability of the lab is achieved. These results should enable important low-frequency applications such as direct intensity-difference imaging with bright beams on integrating detectors.

Optimized phase sensing in a truncated SU(1,1) interferometer.

Homodyne detection is often used for interferometers based on nonlinear optical gain media. For the configuration of a seeded, "truncated SU(1,1)" interferometer Anderson, et al. [ Phys. Rev. A95, 063843 (2017)] showed how to optimize the homodyne detection scheme and demonstrated theoretically that it can saturate the quantum Cramer-Rao bound for phase estimation. In this work we extend those results by taking into account loss in the truncated SU(1,1) interferometer and determining the optimized homodyne detection scheme for phase measurement. Further, we build a truncated SU(1,1) interferometer and experimentally demonstrate that this optimized scheme achieves a reduction in noise level, corresponding to an enhanced potential phase sensitivity, compared to a typical homodyne detection scheme for a two-mode squeezed state. In doing so, we also demonstrate an improvement in the degree to which we can beat the standard quantum limit with this device.

Improved measurement of two-mode quantum correlations using a phase-sensitive amplifier.

We demonstrate the ability of a phase-sensitive amplifier (PSA) to pre-amplify a selected quadrature of one mode of a two-mode squeezed state in order to improve the measurement of two-mode quantum correlations that exist before degradation due to optical and detection losses. We use four-wave mixing (4WM) in 85Rb vapor to generate bright beams in a two-mode squeezed state. One of these two modes then passes through a second 4WM interaction in a PSA configuration to noiselessly pre-amplify the desired quadrature of the mode before loss is intentionally introduced. We demonstrate an enhancement in the measured degree of intensity correlation and intensity-difference squeezing between the two modes.

Pilot Feasibility Study of Therapeutic Hypothermia for Moderate to Severe Acute Respiratory Distress Syndrome.

OBJECTIVES: Prior studies suggest hypothermia may be beneficial in acute respiratory distress syndrome, but cooling causes shivering and increases metabolism. The objective of this study was to assess the feasibility of performing a randomized clinical trial of hypothermia in patients with acute respiratory distress syndrome receiving treatment with neuromuscular blockade because they cannot shiver. DESIGN: Retrospective study and pilot, prospective, open-label, feasibility study. SETTING: Medical ICU. PATIENTS: Retrospective review of 58 patients with acute respiratory distress syndrome based on Berlin criteria and PaO2/FIO2 less than 150 who received neuromuscular blockade. Prospective hypothermia treatment in eight acute respiratory distress syndrome patients with PaO2/FIO2 less than 150 receiving neuromuscular blockade. INTERVENTION: Cooling to 34-36°C for 48 hours. MEASUREMENTS AND MAIN RESULTS: Core temperature, hemodynamics, serum glucose and electrolytes, and P/F were sequentially measured, and medians (interquartile ranges) presented, 28-day ventilator-free days, and hospital mortality were calculated in historical controls and eight cooled patients. Average patient core temperature was 36.7°C (36-37.3°C), and fever occurred during neuromuscular blockade in 30 of 58 retrospective patients. In the prospectively cooled patients, core temperature reached target range less than or equal to 4 hours of initiating cooling, remained less than 36°C for 92% of the 48 hours cooling period without adverse events, and was lower than the controls (34.35°C [34-34.8°C]; p < 0.0001). Compared with historical controls, the cooled patients tended to have lower hospital mortality (75% vs 53.4%; p = 0.26), more ventilator-free days (9 [0-21.5] vs 0 [0-12]; p = 0.16), and higher day 3 P/F (255 [160-270] vs 171 [120-214]; p = 0.024). CONCLUSIONS: Neuromuscular blockade alone does not cause hypothermia but allowed acute respiratory distress syndrome patients to be effectively cooled. Results support conducting a randomized clinical trial of hypothermia in acute respiratory distress syndrome and the feasibility of studying acute respiratory distress syndrome patients receiving neuromuscular blockade.

Effect of input phase modulation to a phase-sensitive optical amplifier.

Many optical applications depend on amplitude modulating optical beams using devices such as acousto-optical modulators (AOMs) or optical choppers. Methods to add amplitude modulation (AM) often inadvertently impart phase modulation (PM) onto the light as well. While this PM is of no consequence to many phase-insensitive applications, phase-sensitive processes can be affected. Here we study the effects of input phase and amplitude modulation on the output of a quantum-noise limited phase-sensitive optical amplifier (PSA) realized in hot 85Rb vapor. We investigate the dependence of PM on AOM alignment and demonstrate a novel approach to quantifying PM by using the PSA as a diagnostic tool. We then use this method to measure the alignment-dependent PM of an optical chopper which arises due to diffraction effects as the chopper blade passes through the optical beam.

Critical Care Resuscitation Unit: An Innovative Solution to Expedite Transfer of Patients with Time-Sensitive Critical Illness.

BACKGROUND: Time-sensitive, critical surgical illnesses require care at specialized centers. Trauma systems facilitate patient transport to designated trauma centers, but formal systems for nontraumatic critical illness do not exist. We created the critical care resuscitation unit to expedite transfers of adult critically ill patients with time-sensitive conditions to a quaternary academic medical center, hypothesizing that this would decrease time to transfer, increase transfer volume, and improve outcomes. STUDY DESIGN: Critical care transfers to the University of Maryland Medical Center during the first year of the critical care resuscitation unit (July 2013 to June 2014) were compared with a previous year (July 2011 to June 2012). Times from transfer request to arrival and operating room and hospital mortality were compared. RESULTS: There was a 64.5% increase in transfers with a 93.6% increase in critically ill surgical patients. For patients requiring operation, median time to arrival and operating room (118 vs 223 minutes and 1,113 vs 3,424 minutes, respectively; p < 0.001 for both) and median hospital length of stay (13 vs 17 days; p < 0.001) were reduced significantly. There was a nonsignificant trend toward lower mortality (14.6% vs 16.5%; p = 0.27). CONCLUSIONS: The critical care resuscitation unit dramatically increased the volume of critically ill surgical patients. It decreased transfer times, increased volume, and, for those who required urgent operation, decreased time from initial referral to operating room. This benefit seems to be most marked in patients needing urgent operation. This might be a paradigm shift expediting the transfer of patients with time-sensitive critical illness to an appropriately resourced specialty center.

Metal-free dihydroxylation of alkenes using cyclobutane malonoyl peroxide.

Cyclobutane malonoyl peroxide (7), prepared in a single step from the commercially available diacid 6, is an effective reagent for the dihydroxylation of alkenes. Reaction of a chloroform solution of 7 with an alkene in the presence of 1 equiv of water at 40 °C followed by alkaline hydrolysis leads to the corresponding diol (30-84%). With 1,2-disubstituted alkenes, the reaction proceeds with syn-selectivity (3:1 → 50:1). A mechanism consistent with experimental findings is proposed, which is supported by deuterium and oxygen labeling studies and explains the stereoselectivity observed. Alternative reaction pathways that are dependent on the structure of the starting alkene are also described leading to the synthesis of allylic alcohols and γ-lactones.

Multi-spatial-mode single-beam quadrature squeezed states of light from four-wave mixing in hot rubidium vapor.

We present experimental results on the generation of multi-spatial-mode, single-beam, quadrature squeezed light using four-wave mixing in hot Rb vapor. Squeezing and phase-sensitive deamplification are observed over a range of powers and detunings near the (85)Rb D1 atomic transition. We observe -3 dB of vacuum quadrature squeezing, comparable to the best single-spatial mode results previously reported using atomic vapors, however, produced here in multiple spatial modes. We confirm that the squeezing is present in more than one transverse mode by studying the spatial distribution of the noise properties of the field.

Alkene syn dihydroxylation with malonoyl peroxides.

Cyclopropyl malonoyl peroxide (1), which can be prepared in a single step from the commercially available diacid, is an effective reagent for the dihydroxylation of alkenes. Reaction of 1 with an alkene in the presence of 1 equiv of water at 40 °C followed by alkaline hydrolysis leads to the corresponding diol (40-93%). With 1,2-disubstituted alkenes, the reaction proceeds with syn selectivity (3:1 to >50:1). A mechanism consistent with the experimental findings that is supported by oxygen-labeling studies is proposed.