Entanglement on an optical atomic-clock transition.

State-of-the-art atomic clocks are based on the precise detection of the energy difference between two atomic levels, which is measured in terms of the quantum phase accumulated over a given time interval1-4. The stability of optical-lattice clocks (OLCs) is limited both by the interrupted interrogation of the atomic system by the local-oscillator laser (Dick noise5) and by the standard quantum limit (SQL) that arises from the quantum noise associated with discrete measurement outcomes. Although schemes for removing the Dick noise have been recently proposed and implemented4,6-8, performance beyond the SQL by engineering quantum correlations (entanglement) between atoms9-20 has been demonstrated only in proof-of-principle experiments with microwave clocks of limited stability. The generation of entanglement on an optical-clock transition and operation of an OLC beyond the SQL represent important goals in quantum metrology, but have not yet been demonstrated experimentally16. Here we report the creation of a many-atom entangled state on an OLC transition, and use it to demonstrate a Ramsey sequence with an Allan deviation below the SQL after subtraction of the local-oscillator noise. We achieve a metrological gain of [Formula: see text] decibels over the SQL by using an ensemble consisting of a few hundred ytterbium-171 atoms, corresponding to a reduction of the averaging time by a factor of 2.8 ± 0.3. Our results are currently limited by the phase noise of the local oscillator and Dick noise, but demonstrate the possible performance improvement in state-of-the-art OLCs1-4 through the use of entanglement. This will enable further advances in timekeeping precision and accuracy, with many scientific and technological applications, including precision tests of the fundamental laws of physics21-23, geodesy24-26 and gravitational-wave detection27.

Search for Ultralight Dark Matter from Long-Term Frequency Comparisons of Optical and Microwave Atomic Clocks.

We search for ultralight scalar dark matter candidates that induce oscillations of the fine structure constant, the electron and quark masses, and the quantum chromodynamics energy scale with frequency comparison data between a ^{171}Yb optical lattice clock and a ^{133}Cs fountain microwave clock that span 298 days with an uptime of 15.4%. New limits on the couplings of the scalar dark matter to electrons and gluons in the mass range from 10^{-22} to 10^{-20} eV/c^{2} are set, assuming that each of these couplings is the dominant source of the modulation in the frequency ratio. The absolute frequency of the ^{171}Yb clock transition is also determined as 518 295 836 590 863.69(28) Hz, which is one of the important contributions toward a redefinition of the second in the International System of Units.

Evidence of Two-Source King Plot Nonlinearity in Spectroscopic Search for New Boson.

Optical precision spectroscopy of isotope shifts can be used to test for new forces beyond the standard model, and to determine basic properties of atomic nuclei. We measure isotope shifts on the highly forbidden ^{2}S_{1/2}→^{2}F_{7/2} octupole transition of trapped ^{168,170,172,174,176}Yb ions. When combined with previous measurements in Yb^{+} and very recent measurements in Yb, the data reveal a King plot nonlinearity of up to 240σ. The trends exhibited by experimental data are explained by nuclear density functional theory calculations with the Fayans functional. We also find, with 4.3σ confidence, that there is a second distinct source of nonlinearity, and discuss its possible origin.

Evidence for Nonlinear Isotope Shift in Yb

We measure isotope shifts for five Yb^{+} isotopes with zero nuclear spin on two narrow optical quadrupole transitions ^{2}S_{1/2}→^{2}D_{3/2}, ^{2}S_{1/2}→^{2}D_{5/2} with an accuracy of ∼300 Hz. The corresponding King plot shows a 3×10^{-7} deviation from linearity at the 3σ uncertainty level. Such a nonlinearity can indicate physics beyond the Standard Model (SM) in the form of a new bosonic force carrier, or arise from higher-order nuclear effects within the SM. We identify the quadratic field shift as a possible nuclear contributor to the nonlinearity at the observed scale, and show how the nonlinearity pattern can be used in future, more accurate measurements to separate a new-boson signal from nuclear effects.

Robust kHz-linewidth distributed Bragg reflector laser with optoelectronic feedback.

We demonstrate a combination of optical and electronic feedback that significantly narrows the linewidth of distributed Bragg reflector lasers (DBRs). We use optical feedback from a long external fiber path to reduce the high-frequency noise of the laser. An electro-optic modulator placed inside the optical feedback path allows us to apply electronic feedback to the laser frequency with very large bandwidth, enabling robust and stable locking to a reference cavity that suppresses low-frequency components of laser noise. The combination of optical and electronic feedback allows us to significantly lower the frequency noise power spectral density of the laser across all frequencies and narrow its linewidth from a free-running value of 1.1 MHz to a stabilized value of 1.9 kHz, limited by the detection system resolution. This approach enables the construction of robust lasers with sub-kHz linewidth based on DBRs across a broad range of wavelengths.

Near-Unitary Spin Squeezing in

Spin squeezing can improve atomic precision measurements beyond the standard quantum limit (SQL), and unitary spin squeezing is essential for improving atomic clocks. We report substantial and nearly unitary spin squeezing in ^{171}Yb, an optical lattice clock atom. The collective nuclear spin of ∼10^{3} atoms is squeezed by cavity feedback, using light detuned from the system's resonances to attain unitarity. The observed precision gain over the SQL is limited by state readout to 6.5(4) dB, while the generated states offer a gain of 12.9(6) dB, limited by the curvature of the Bloch sphere. Using a squeezed state within 30% of unitarity, we demonstrate an interferometer that improves the averaging time over the SQL by a factor of 3.7(2). In the future, the squeezing can be simply transferred onto the optical-clock transition of ^{171}Yb.

Change in the crystalline structure during the phase transition of the palladium-hydrogen system.

We performed an X-ray diffraction experiment while a palladium bulk absorbed and desorbed hydrogen to investigate the behavior of the crystalline lattice during the phase transition between the α phase and the ß phase. Fast growth of the ß phase was observed at around x = 0.1 and x = 0.45 of PdHx, and the phase transition rate has an exponential behavior in between. In addition, slight compression of the lattice at a high hydrogen concentration, an increase in the lattice constant, and broadening of the line width of the α phase after a cycle of absorption and desorption of hydrogen were observed. These behaviors correlated with the change in the sample length, which may infer that the change in shape was related to the phase transition.

Passive intrinsic-linewidth narrowing of ultraviolet extended-cavity diode laser by weak optical feedback.

We present a simple method for narrowing the intrinsic Lorentzian linewidth of a commercial ultraviolet grating extended-cavity diode laser (TOPTICA DL Pro) using weak optical feedback from a long external cavity. We achieve a suppression in frequency noise spectral density of 20 dB measured at frequencies around 1 MHz, corresponding to the narrowing of the intrinsic Lorentzian linewidth from 200 kHz to 2 kHz. Provided additional active low-frequency noise suppression and long-term drift compensation, the system is suitable for experiments requiring a tunable ultraviolet laser with narrow linewidth and low high-frequency noise, such as precision spectroscopy, optical clocks, and quantum information science experiments.

Dipole moment background measurement and suppression for levitated charge sensors.

Optically levitated macroscopic objects are a powerful tool in the field of force sensing, owing to high sensitivity, absolute force calibration, environmental isolation, and the advanced degree of control over their dynamics that have been achieved. However, limitations arise from the spurious forces caused by electrical polarization effects that, even for nominally neutral objects, affect the force sensing because of the interaction of dipole moments with gradients of external electric fields. Here, we introduce a technique to measure, model, and eliminate dipole moment interactions, limiting the performance of sensors using levitated objects. This process leads to a noise-limited measurement with a sensitivity of 3.3 × 10-5 e. As a demonstration, this is applied to the search for unknown charges of a magnitude much below that of an electron or for exceedingly small unbalances between electron and proton charges.

The exquisite structure and reaction mechanism of bacterial Pz-peptidase A toward collagenous peptides: X-ray crystallographic structure analysis of PZ-peptidase a reveals differences from mammalian thimet oligopeptidase.

Pz-peptidase A, from the thermophilic bacterium Geobacillus collagenovorans MO-1, hydrolyzes a synthetic peptide substrate, 4-phenylazobenzyloxycarbonyl-Pro-Leu-Gly-Pro-D-Arg (Pz-PLGPR), which contains a collagen-specific tripeptide sequence, -Gly-Pro-X-, but does not act on collagen proteins themselves. The mammalian enzyme, thimet oligopeptidase (TOP), which has comparable functions with bacterial Pz-peptidases but limited identity at the primary sequence level, has recently been subjected to x-ray crystallographic analysis; however, no crystal structure has yet been reported for complexes of TOP with substrate analogues. Here, we report crystallization of recombinant Pz-peptidase A in complex with two phosphinic peptide inhibitors (PPIs) that also function as inhibitors of TOP and determination of the crystal structure of these complexes at 1.80-2.00 Å resolution. The most striking difference between Pz-peptidase A and TOP is that there is no channel running the length of bacterial protein. Whereas the structure of TOP resembles an open bivalve, that of Pz-peptidase A is closed and globular. This suggests that collagenous peptide substrates enter the tunnel at the top gateway of the closed Pz-peptidase A molecule, and reactant peptides are released from the bottom gateway after cleavage at the active site located in the center of the tunnel. One of the two PPIs, PPI-2, which contains the collagen-specific sequence, helped to clarify the exquisite structure and reaction mechanism of Pz-peptidase A toward collagenous peptides. This study describes the mode of substrate binding and its implication for the mammalian enzymes.

Papillary muscle sandwich plasty for the treatment of functional mitral valve regurgitation.

We evaluated the availability of original "sandwich plasty" for the treatment of functional mitral regurgitation (FMR) associated with ischemic heart disease (IHD) and aortic valve disease (AVD). Forty-three patients were reviewed, including 27 IHD patients and 16 AVD patients. Preoperatively severe FMR was detected in 14 patients, moderate FMR in 26, and mild FMR in 3. The papillary muscle heads of anterior leaflets and posterior leaflets were approximated using Teflon-pledgeted 3-0 Ticron sutures at anterolateral and posteromedial commissural portions. After surgery, residual moderate FMR was observed in 1 patient and mild FMR in 3 patients. Tenting height of the mitral valve significantly decreased. FMR free rates 2 years after surgery were 93% among IHD patients and 83% in AVD patients. "Sandwich plasty" was simple and effective for the treatment of functional FMR caused by tethering effects due to left ventricular dilatation.

High sensitivity, levitated microsphere apparatus for short-distance force measurements.

A high sensitivity force sensor based on dielectric microspheres in vacuum, optically trapped by a single, upward-propagating laser beam, is described. Off-axis parabolic mirrors are used both to focus the 1064 nm trapping beam and to recollimate it to provide information on the horizontal position of the microsphere. The vertical degree of freedom is readout by forming an interferometer between the light retroreflected by the microsphere and a reference beam, hence eliminating the need for auxiliary beams. The focus of the trapping beam has a 1/E2 radius of 3.2 µm and small non-Gaussian tails, suitable for bringing devices close to the trapped microsphere without disturbing the optical field. Electrodes surrounding the trapping region provide excellent control of the electric field, which can be used to drive the translational degrees of freedom of a charged microsphere and the rotational degrees of freedom of a neutral microsphere, coupling to its electric dipole moment. With this control, the charge state can be determined with single electron precision, the mass of individual microspheres can be measured, and empirical calibrations of the force sensitivity can be made for each microsphere. A force noise of <1 × 10-17 N/Hz, which is comparable to previous reports, is measured on all three degrees of freedom for 4.7 µm diameter, 84 pg silica microspheres. Various devices have been brought within 1.6 µm of the surface of a trapped microsphere. Metrology in the trapping region is provided by two custom-designed microscopes providing views in the horizontal and one of the vertical planes. The apparatus opens the way to performing high sensitivity three-dimensional force measurements at a short distance.

Crystallization and preliminary X-ray crystallographic studies of Pz peptidase A from Geobacillus collagenovorans MO-1.

Pz peptidase A is an intracellular M3 metallopeptidase found in the thermophile Geobacillus collagenovorans MO-1 that recognizes collagen-specific tripeptide units (Gly-Pro-Xaa). Pz peptidase A shares common reactions with mammalian thimet oligopeptidase (TOP) and neurolysin, but has extremely low primary sequence identity to these enzymes. In this work, Pz peptidase A was cocrystallized with a phosphine peptide inhibitor (PPI) that selectively inhibits TOP and neurolysin. The crystals belong to space group P2(1), with unit-cell parameters a = 56.38, b = 194.15, c = 59.93 A, beta = 106.22 degrees . This is the first crystallographic study of an M3 family peptidase-PPI complex.

Septal-superior exposure in mitral valve surgery with radiofrequency ablation.

BACKGROUND: We review the results of surgical radiofrequency ablation of both atria in patients of mitral valve disease approached by septal-superior exposure and discuss the availability of this approach. METHODS: Eighteen patients with a mean age of 65 years were included in this study. Thirteen patients had mitral valve regurgitation predominantly and five had mitral valve stenosis. Eleven patients underwent mitral valve plasty and valve replacement was carried out in seven. All ablation lesions were created on both atria using radiofrequency energy delivered by a unipolar malleable radiofrequency ablation catheter with seven electrodes at a minimum temperature of 80-85 degrees C for a period of 2 min. RESULTS: At the time of discharge, 14 patients were showed normal sinus rhythm and one patient remained in AF. The other three patients were free from atrial fibrillation; however, they received dual-mode, dual-pacing, dual-sensing pacemaker implantation because of bradycardia during the early postoperative phase. At a mean time of 7 months after surgery, all patients were free from atrial fibrillation; 13 patients showed normal sinus rhythm and five patients received dual-mode, dual-pacing, dual-sensing pacemakers. CONCLUSION: Septal-superior exposure provides an excellent operative view both for mitral valve surgery and for radiofrequency ablation. However, this exposure has not been considered a first-line approach because of the high rate of pacemaker implantation.

Resistance of zwitterionic telomers accumulated on metal surfaces against nonspecific adsorption of proteins.

Telomers of N,N-dimethyl-N-(3-sulfopropyl)-3'-methacryloylaminopropanaminium inner salt (SPB), 2-methacryloyloxyethyl phosphorylcholine (MPC), and N,N-dimethyl-N-(1-carboxymethyl)-2'-methacryloyloxylethanaminium inner salt (CMB) were prepared by UV irradiation in the presence of N,N,N',N'-tetraethylthiuram disulfide and a disulfide-group-carrying iniferter (a compound which pursues initiation, chain transfer, and termination), Cys-BDC, which had been prepared by coupling N,N-diethyldithiocarbamoylmethylbenzoic acid succinimidyl ester with cystamine dihydrochloride. The telomers formed a self-assembled monolayer (SAM) on a gold electrode and a monolayer of colloidal gold deposited on a glass plate, as confirmed by the increase in potential difference (DeltaE(p)) of the voltammogram for hydroquinone as a probe using cyclic voltammetry (CV) and the increase in absorbance using localized surface plasmon resonance (LSPR) absorption spectroscopy, respectively. Nonspecific adsorption of various proteins onto the surfaces of various telomer SAMs was examined from the decrease in peak current (DeltaI) using CV and the absorption increase at 550 nm using LSPR absorption spectroscopy. The zwitterionic telomer SAM in general did not adsorb proteins significantly, suggesting the usability of zwitterionic polymer SAMs and brushes to coat various materials used in biomedical fields. The correlation between the structure of water in the vicinity of zwitterionic telomers and the resistance of the zwitterionic telomer SAMs against the nonspecific adsorption of proteins was discussed.

Note: Fast compact laser shutter using a direct current motor and three-dimensional printing.

We present a mechanical laser shutter design that utilizes a direct current electric motor to rotate a blade which blocks and unblocks a light beam. The blade and the main body of the shutter are modeled with computer aided design (CAD) and are produced by 3D printing. Rubber flaps are used to limit the blade's range of motion, reducing vibrations and preventing undesirable blade oscillations. At its nominal operating voltage, the shutter achieves a switching speed of (1.22 ± 0.02) m/s with 1 ms activation delay and 10 µs jitter in its timing performance. The shutter design is simple, easy to replicate, and highly reliable, showing no failure or degradation in performance over more than 10(8) cycles.

Effects of original crystalloid cardioplegia followed by additional blood cardioplegia: treatments for prolonged cardiac arrest.

PURPOSE: The efficacy of combination treatment of original cold crystalloid cardioplegia (SHA solution; St. Thomas + Histidine + ATP + oxygen) and additional blood cardioplegia was studied in patients who required cardiac arrest time of 120 minutes or longer. METHODS: One hundred and thirty-six patients were included in this study. Patients were divided into two groups according to the cardiac arrest time: S group (cardiac arrest time: 120-149 minutes, n = 81); L group (150-180 minutes, n = 55). Just after cross-clamping of the ascending aorta, 800 ml of SHA solution was infused in an antegrade fashion. Cold-blood cardioplegia was initiated after two hours of cardiac arrest. RESULTS: Six (4%) of the 136 patients died after surgery, 3 in each group. Two critical patients with ischemic cardiomyopathy died of cardiac failure after coronary artery bypass grafting (CABG), and 4 died of noncardiac morbidity. The mean value of postoperative maximum creatine phosphokinase-MB (CPK-MB) in dead patients was 47 IU/L in the S group and 75 IU/L in the L group. The peak CPK-MB values exceeded 100 IU/L in one out of 6 patients who died after surgery. CONCLUSIONS: Combination treatment using original SHA solution and additional blood cardioplegia was effective in patients who required prolonged cardiac arrest.

Surgical treatments for infective endocarditis involving valve annulus.

OBJECTIVE: The early and late results of infective endocarditis (IE) with annular involvement were studied by focusing on surgical findings and operative procedures. MATERIALS AND METHODS: Fifteen adult patients with a mean age of 56 years were reviewed. Eight had native valve endocarditis (NVE), and 7 had prosthetic valve endocarditis (PVE). The diseased valve was mitral in 6 patients, aortic in 8, and mitral plus aortic in 1. Twelve patients were operated on during the active phase of IE. Enterococcus, Staphyrococcus, Streptococcus, and Stenotrophomonaus Maltophilia were predominant in bacterial examination. The mean follow-up period was 37 months. RESULTS: Active vegetation was observed in 63% of total patients. In NVE patients, valve replacement was performed in all 8 after complete debridement and annular patch reconstruction. One patient with hemodialysis died of heart failure. In PVE patients, valve deficiency was observed in all and active perivalvular abscess in 4. Conventional valve replacement was performed in 4 patients, and 3 of them died after surgery. Three patients who underwent aortic root translocation or Ross procedure survived. The hospital mortality of NVE and PVE surgery was 3% and 43%, respectively. There were no significant correlations between operative results and perioperative factors. During the follow-up period, late recurrent endocarditis did not occur, and one patient died of noncardiac diseases. CONCLUSION: For NVE, good operative results were obtained after complete resection of infected valve annulus and valve replacement. For PVE, new surgical treatments, such as the translocation method or Ross procedure, should be induced for further improvement of surgical results.

Original papillary muscle sandwich plasty for ischemic mitral regurgitation.

BACKGROUND: Mitral valve plasty for functional ischemic mitral regurgitation (MR) is still a controversial procedure. METHODS AND RESULTS: The present study was a review of 23 patients who underwent an original technique known as "papillary muscle sandwich plasty" in which the mitral valve is approached via either the left atrium or left ventricle. The heads of the papillary muscles of the anterior leaflet and leaflets are plicated using Teflon-pledgeted 3-0 Ticron sutures in both the anterolateral and posteromedial commissural portions. Postoperative residual mild MR occurred in 1 patient (4%), but moderate or severe MR was not observed. In the follow-up study, prominent MR occurred in 1 patients and the MR-free rate at 2 years after surgery was 93%. Late cardiac death was significantly (P<0.05) fewer in patients without prominent MR than that in patients with MR. CONCLUSIONS: "Sandwich plasty" is an effective technique for patients requiring left ventricular plasty and may improve the prognosis of ischemic heart failure.

Combined surgery for ischemic cardiomyopathy: report of a case.

A 65-year-old female with catecholamine-dependent ischemic cardiomyopathy was admitted to our hospital. Preoperative examination revealed severe triple vessel coronary artery disease, severe mitral valve regurgitation and left ventricular (LV) dilatation associated with low ejection fraction. Coronary artery bypass grafting with four distal anastomoses, mitral valve plasty using original papillary muscle application method, LV volume reduction using overlapping method and biventricular pacing were performed. Postoperative course was uneventful and quality of life at 2 years after surgery was good. Active combined surgery has the possibility of improving the outcome of patients with severe ischemic cardiomyopathy.