Session E08: Low Energy Precision Physics Tests

Live

Polar molecules are highly sensitive to a wide variety of fundamental symmetry violations in the leptonic and hadronic sectors, and are currently the most sensitive probes of the electron EDM. However, many advantages of molecules are yet to be realized, including the application of advanced quantum control methods, and extending symmetry violation searches beyond the electron EDM, both of which offer the ability to extend the reach of experiments by orders of magnitude -- far beyond the reach of direct searches. In this talk, we discuss how polyatomic molecules offer unique advantages for a variety of symmetry violation searches, including the electron EDM, nuclear magnetic quadrupole moments, and nuclear Schiff moments. The unique, symmetry-lowering mechanical modes of polyatomic molecules makes them highly polarizable and amenable to techniques for robust rejection of systematic effects. As these mechanical modes do not rely strongly on electronic structure, these advantages can be realized in a wide variety of nuclei with few restrictions. We will give updates on experimental and theoretical efforts in our lab to search for these symmetry violations, and to identify new molecules and methods for sensitive measurements of many sources of new fundamental physics.   

Live

Trapped ultracold molecules are a potentially powerful platform for probing physics beyond the Standard Model. YbOH, which has recently been laser cooled in one dimension to $<$600 $\mu$K, is predicted to have high sensitivity to the electron's electric dipole moment. Here, we report on work aiming to achieve laser cooling and trapping of large numbers of molecules in three dimensions. We have constructed a He-3-based cryogenic beam source with the goal of achieving forward velocities below 30 m/s and a superconducting Zeeman-Sisyphus decelerator designed to slow molecules to trappable velocities using just three photon scatters. To increase the number of molecules that could be trapped, we use a laser-assisted chemical reaction between Yb and H$_2$O to enhance molecular beam flux by more than an order of magnitude. We also present ultra-high-sensitivity measurements of vibrational branching ratios in YbOH, identifying vibrational states relevant for laser cooling using up to scattered $10^5$ photons. From these measurements, we determine a feasible laser cooling scheme to achieve temperatures below the Doppler limit.   

Live

Studying the effect of gravity on massive quantum systems calls for the preparation of quantum states of objects massive enough to be noticeably susceptible to gravity. However, quantum behavior in macroscopic systems is greatly impeded by interactions with the thermal environment. Traditional techniques, such as laser sideband cooling, that are able to realize quantum states of motion of atomic and nano-scale objects do not work for kilogram-scale objects. We employ the exceptional displacement sensitivity of Advanced LIGO to resolve the zero-point motion of a $10$ kg mechanical oscillator with a precision sufficient to feedback cool its motion to $10.8$ phonons on average. The reduction in oscillator temperature, from room temperature to $77$ nK, represents a 100-fold improvement in the reduction of temperature of a solid-state mechanical oscillator---commensurate with a 11 orders-of-magnitude suppression of quantum back-action by feedback---and a 10 orders-of-magnitude increase in the mass of an object prepared close to its motional ground state.   

Live

Gravity is the weakest of all known fundamental forces and continues to pose some of the most outstanding open problems to modern physics: it remains resistant to unification within the standard model of physics and its underlying concepts appear to be fundamentally disconnected from quantum theory. Testing gravity on all scales is therefore an important experimental endeavour. Thus far, these tests involve mainly macroscopic masses on the kg-scale and beyond. Here we show gravitational coupling between two gold spheres of 1mm radius, thereby entering the regime of sub-100mg sources of gravity. Periodic modulation of the source mass position allows us to perform a spatial mapping of the gravitational force. Both linear and quadratic coupling are observed as a consequence of the nonlinearity of the gravitational potential. Our results extend the parameter space of gravity measurements to small single source masses and small gravitational field strengths. Further improvements will enable the isolation of gravity as a coupling force for objects below the Planck mass. This opens the way to a yet unexplored frontier of microscopic source masses, which enables new searches of fundamental interactions and provides a natural path towards exploring the quantum nature of gravity.   

Live

The electric potential induced by an optical tweezer about the focal point approximates a simple harmonic potential. An optically trapped nanoparticle in the ground state of this potential could provide a very valuable tool for ultrasensitive force detection, such as probing weak gravitational interaction. Primarily two cooling methods, parametric feedback cooling of the trapping laser and cavity sideband cooling, have been experimentally implemented to lower the harmonic energy state of the nanoparticle. Fundamental limitations place constraints to the effectiveness of these two methods. One such limitation occurs by increasing the trapping laser power, the strength of cooling increases but also consequently increases the internal temperature of the nanoparticle. The current project looks to trap a quantum dot while optically cooling it to address this effect. If placing this quantum dot in an ultrahigh vacuum environment, sequentially applying parametric feedback and then cavity sideband cooling proves successful, theoretically, this proposed scheme should cool to the ground state and provide a way to further the search for non-Newtonian forces and explore other short-range interaction physics.   

Live

We have developed a torsion balance with a sensitivity about ten times better than those of previously operating balances for the study of long range forces coupling to baryon and lepton numbers. This talk will present the details of the design and expected performance of this balance in an experiment searching for a violation of Einstein's equivalence principle. Operation of this balance for a year is also expected to result in improved bounds on long range interactions of dark matter violating the equivalence principle.   

Live

Precise determination of Newtonian gravitational constant {\it G} is challenging when compared to other universal constants due to its extremely weak interaction strength. Meanwhile, more questions are raised in the accuracy among the {\it G} measurements as results disagree with each other. To improve the situation, a new apparatus based on the angular-acceleration-feedback torsion pendulum system has been designed and is being assembled in our lab. A precision about 2 ppm will be mainly achieved by increasing the system size, which reduces the metrological uncertainty. The disagreement among different approaches will be investigated by integrating another two modes into the same apparatus, ({\it i}) the time-of-swing method with large amplitudes and ({\it ii}) extracting the resonance frequency of the pendulum through noise measurements. The idea is to address the potential Kuroda effect by comparing {\it G} determined by three different methods in the same apparatus. The progress of the construction with system characterization data will be shown in the presentation.   

Live

I point out that in models of macroscopic topological defects composed of one or more scalar fields that interact non-gravitationally with standard-model fields via scalar-type couplings, the previously overlooked ``back action'' of ambient matter on the scalar field(s) produces an environmental dependence of the fundamental constants of nature as well as spatial variations of the fundamental constants in the vicinity of dense bodies such as Earth due to the formation of a ``bubblelike'' defect structure surrounding the dense body. I have derived bounds on non-transient variations of the fundamental constants from torsion-pendulum experiments that search for equivalence-principle-violating forces, experiments comparing the frequencies of ground- and space-based atomic clocks as well as ground-based clocks at different heights in the recent Tokyo SKYTREE experiment, and measurements comparing atomic and molecular transition frequencies in laboratory and low-density astrophysical environments. My newly derived bounds on scalar-field domain walls are significantly more stringent than previously reported bounds, including bounds from clock-based searches for passing domain walls via transient signatures, under the same set of assumptions. Reference: [Stadnik, PRD 102, 115016 (2020)]   

Live

We introduce a new interpretation of quantum mechanics by examining the Einstein, Podolsky and Rosen's (EPR) paradox and Bell's inequality experiments under the assumption that the vacuum has an inhomogeneous texture for energy levels below the Heisenberg time-energy uncertainty relation. In this talk, selected results from the most reliable Bell's inequality experiments will be quantitatively analyzed to show that our interpretation of quantum mechanics creates a new loophole in Bell's inequality, and that the past experimental findings do not contradict our new interpretation. Under the vacuum texture interpretation of quantum mechanics in a Bell's inequality experiment, the states of the pair of particles created at the source (e.g. during parametric downconversion) is influenced by an inhomogeneous vacuum texture sent from the measurement apparatus. We will also show that the resulting pair of particles is not entangled and that the theory of vacuum texture preserves local realism with complete causality. This talk will also suggest an experiment to definitively confirm the existence of vacuum texture. https://arxiv.org/abs/1905.04340