The evolution of a quantum state undergoing radiative decay depends on how its emission is detected. If the emission is detected in the form of energy quanta, the evolution is characterized by a quantum jump to a lower energy state. In contrast, detection of the wave nature of the emitted radiation leads to different dynamics. Here, we investigate the diffusive dynamics of a superconducting artificial atom under continuous homodyne detection of its spontaneous emission. Using quantum state tomography, we characterize the correlation between the detected homodyne signal and the emitter's state, and map out the conditional back-action of homodyne measurement. By tracking the diffusive quantum trajectories of the state as it decays, we characterize selective stochastic excitation induced by the choice of measurement basis. Our results demonstrate dramatic differences from the quantum jump evolution associated with photodetection and highlight how continuous field detection can be harnessed to control quantum evolution.
We use narrow-band laser excitation of Yb atoms to substantially enhance the brightness of a cold beam of YbOH, a polyatomic molecule with high sensitivity to physics beyond the standard model (BSM). By exciting atomic Yb to the metastable 3 P 1 state in a cryogenic environment, we significantly increase the chemical reaction cross-section for collisions of Yb with reactants. We characterize the dependence of the enhancement on the properties of the laser light, and study the final state distribution of the YbOH products. The resulting bright, cold YbOH beam can be used to increase the statistical sensitivity in searches for new physics utilizing YbOH, such as electron electric dipole moment and nuclear magnetic quadrupole moment experiments. We also perform new quantum chemical calculations that confirm the enhanced reactivity observed in our experiment and compare reaction pathways of Yb( 3 P) with the reactants H 2 O and H 2 O 2 . More generally, our work presents a broad approach for improving experiments that use cryogenic molecular beams for laser cooling and precision measurement searches of BSM physics.
We describe the design of a cryogenic rotation stage (CRS) for use with the cryogenic half-wave plate (CHWP) polarization modulator on the POLARBEAR-2b and POLARBEAR-2c (PB2b/c) cosmic microwave background (CMB) experiments, the second and third installments of the Simons Array. Rapid modulation of the CMB polarization signal using a CHWP suppresses 1/f contamination due to atmospheric turbulence and allows a single polarimeter to measure both polarization states, mitigating systematic effects that arise when differencing orthogonal detectors. To modulate the full detector array while avoiding excess photon loading due to thermal emission, the CHWP must have a clear-aperture diameter of > 450 mm and be cooled to < 100 K. We have designed a 454-mm-clear-aperture, < 65 K CRS using a superconducting magnetic bearing driven by a synchronous magnetic motor. We present the specifications for the CRS, its interfacing to the PB2b/c receiver cryostat, its performance in a stand-alone test, and plans for future work.Cosmic microwave background (CMB) polarization is a powerful probe of cosmology. Particularly, the "B-mode" CMB polarization pattern can be used to probe gravitational lensing on arcminute angular scales [1, 2] and primordial gravitational waves on degree angular scales [3][4][5]. In order for a single telescope to characterize small and large scales simultaneously, it must observe with high resolution over a large sky area, requiring both a large primary aperture and good low-frequency (or "1/f") noise performance [6].Rapidly-rotating half-wave plates (HWP) are a common technique to modulate CMB polarization and reduce the impact of low-frequency noise on experiment sensitivity [6][7][8][9][10][11][12].
The odd isotopologues of ytterbium monohydroxide, 171,173 YbOH, have been identified as promising molecules in which to measure parity (P) and time reversal (T) violating physics. Here we characterize the 22 1/2 (0,0,0) (0,0,0) AX + − band near 577 nm for these odd isotopologues. Both laser-induced fluorescence (LIF) excitation spectra of a supersonic molecular beam sample and absorption spectra of a cryogenic buffer-gas cooled sample were recorded. Additionally, a novel spectroscopic technique based on laser-enhanced chemical reactions is demonstrated and utilized in the absorption measurements. This technique is especially powerful for disentangling congested spectra. An effective Hamiltonian model is used to extract the fine and hyperfine parameters for the 2 1/2 (0,0,0) A and 2 (0,0,0) X + states. A comparison of the determined 2 (0,0,0) X + hyperfine parameters with recently predicted values (M. Denis, et al.,
Polyatomic molecules have been identified as sensitive probes of charge-parity violating and parity violating physics beyond the Standard Model (BSM). For example, many linear triatomic molecules are both laser-coolable and have parity doublets in the ground electronic X 2Σ+(010) state arising from the bending vibration, both features that can greatly aid BSM searches. Understanding the X 2Σ+(010) state is a crucial prerequisite to precision measurements with linear polyatomic molecules. Here, we characterize the fundamental bending vibration of 174YbOH using high-resolution optical spectroscopy on the nominally forbidden X 2Σ+(010) → Α 2Π1/2(000) transition at 588 nm. We assign 39 transitions originating from the lowest rotational levels of the X 2Σ+(010) state, and accurately model the state's structure with an effective Hamiltonian using best-fit parameters. Additionally, we perform Stark and Zeeman spectroscopy on the X 2Σ+(010) state and fit the molecule-frame dipole moment to D mol = 2.16(1) D and the effective electron g-factor to gS = 2.07(2). Further, we use an empirical model to explain observed anomalous line intensities in terms of interference from spin-orbit and vibronic perturbations in the excited Α 2Π1/2(000) state. Our work is an essential step toward searches for BSM physics in YbOH and other linear polyatomic molecules.
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