Boris Braverman

Carving Complex Many-Atom Entangled States by Single-Photon Detection

We propose a versatile and efficient method to generate a broad class of complex entangled states of many atoms via the detection of a single photon. For an atomic ensemble contained in a strongly coupled optical cavity illuminated by weak single- or multifrequency light, the atom-light interaction entangles the frequency spectrum of a transmitted photon with the collective spin of the atomic ensemble. Simple time-resolved detection of the transmitted photon then projects the atomic ensemble into a desired pure entangled state. This method can be implemented with existing technology, yields high success probability per trial, and can generate complex entangled states such as mesoscopic superposition states of coherent spin states with high fidelity.

Preventing and reversing vacuum-induced optical losses in high-finesse tantalum (V) oxide mirror coatings.

High-finesse optical cavities placed under vacuum are foundational platforms in quantum information science with photons and atoms. We study the vacuum-induced degradation of high-finesse optical cavities with mirror coatings composed of SiO₂-Ta₂O₅ dielectric stacks, and present methods to protect these coatings and to recover their initial low loss levels. For separate coatings with reflectivities centered at 370 nm and 422 nm, a vacuum-induced continuous increase in optical loss occurs if the surface-layer coating is made of Ta₂O₅, while it does not occur if it is made of SiO₂. The incurred optical loss can be reversed by filling the vacuum chamber with oxygen at atmospheric pressure, and the recovery rate can be strongly accelerated by continuous laser illumination at 422 nm. Both the degradation and the recovery processes depend strongly on temperature. We find that a 1 nm-thick layer of SiO₂ passivating the Ta₂O₅ surface layer is sufficient to reduce the degradation rate by more than a factor of 10, strongly supporting surface oxygen depletion as the primary degradation mechanism.

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.

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 blades 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.

A comparison of phase, amplitude, and velocity binning for cone-beam computed tomographic projection-based motion reconstruction

PURPOSE We previously developed a motion estimation technique based on direct cone-beam projection analysis. It is able to reconstruct the complete motion trajectory of a radio-opaque marker, including cycle-to-cycle variability, using respiratory binning of the projection images. This paper investigates the use of phase, amplitude, and amplitude-velocity binning in the context of projection-based cone-beam motion estimation (CBME). METHODS AND MATERIALS We simulated cone-beam computed tomographic scans of 160 tumor trajectories estimated by a CyberKnife Synchrony System (Accuray, Sunnyvale, CA), and reconstructed the complete trajectory with CBME using phase, amplitude, and amplitude-velocity binning of the projection data. Various numbers of respiratory bins, from 1 (no binning) to 100, were used for phase and amplitude binning, while 1 to 100 amplitude bins with 4 velocity bins were used for amplitude-velocity binning. From this large pool of data, we correlated the reconstruction accuracy with bin type, total number of bins, number of breathing cycles per bin, and the position of the bin within the breathing cycle. RESULTS CBME predicted the true motion of the marker with a 3-dimensional (3D) mean root mean square (RMS) error of 0.24 mm for amplitude-velocity binning, 0.31 mm for amplitude binning, and 0.52 mm for phase binning. Reconstruction 3D RMS error increased to over 1 mm when less than 3 breathing cycles contributed to a bin. We found that reconstruction accuracy was optimized when about 20 bins were used. Accuracy also decreased in bins located around the inhale portion of the breath cycle, compared with the mid- and end-exhale positions. CONCLUSIONS This study provides a quantitative assessment of phase, amplitude, and amplitude-velocity binning for CBME. A joint binning approach should be used to give both the accuracy of amplitude binning, as well as the robustness of phase binning, in areas of limited motion sampling.

Impact of non-unitary spin squeezing on atomic clock performance

Spin squeezing is a form of entanglement that can improve the stability of quantum sensors operating with multiple particles, by inducing inter-particle correlations that redistribute the quantum projection noise. Previous analyses of potential metrological gain when using spin squeezing were performed on theoretically ideal states, without incorporating experimental imperfections or inherent limitations which result in non-unitary quantum state evolution. Here, we show that potential gains in clock stability are substantially reduced when the spin squeezing is non-unitary, and derive analytic formulas for the clock performance as a function of squeezing, excess spin noise, and interferometer contrast. Our results highlight the importance of creating and employing nearly pure entangled states for improving atomic clocks.

Two-Color Magneto-Optical Trap with Small Magnetic Field for Ytterbium

We report a two-color magneto-optical trap (MOT) for ytterbium atoms operating at a low magnetic field gradient down to 2 G/cm where a conventional MOT using the singlet transition (6s^2 1S0 -> 6s6p 1P1) is unable to trap atoms. By simultaneously applying laser light on both the broad-linewidth singlet transition and the narrow-linewidth triplet transition (6s^2 1S0 -> 6s6p 3P1), we load and trap 4.0 x 10^5 atoms directly from an atomic beam at 700 K. In the two-color MOT, the slowing and trapping functions are separately performed by the singlet transition light and the triplet transition light, respectively. The two-color MOT is highly robust against laser power imbalance even at very low magnetic field gradients.

Measuring Bohm Trajectories of Entangled Photons

We measure, using weak measurement, the Bohmian trajectories of one photon that is part of an entangled pair. Our results shed light on the nonlocality of the Bohm model, as well as its so-called “surrealism”.