Permanent Electric Dipole Research Articles

An ultracold heavy Rydberg system formed from ultra-long-range molecules bound in a stairwell potential

We propose a scheme to realize a heavy Rydberg system (HRS), a bound pair of oppositely charged ions, from a gas of ultracold atoms. The intermediate step to achieve large internuclear separations is the creation of a unique class of ultra-long-range Rydberg molecules bound in a stairwell potential energy curve. Here, a ground-state atom is bound to a Rydberg atom in an oscillatory potential emerging due to attractive singlet p-wave electron scattering. The utility of our approach originates in the large electronic dipole transition element between the Rydberg and the ionic molecule, while the nuclear configuration of the ultracold gas is preserved. The Rabi coupling between the Rydberg molecule and the heavy Rydberg system is typically in the MHz range and the permanent electric dipole moments of the HRS can be as large as one kilo-Debye. We identify specific transitions which place the creation of the heavy Rydberg system within immediate reach of experimental realization.

Electrically tunable topological transport of moiré polaritons

Moiré interlayer exciton in transition metal dichalcogenide heterobilayer features a permanent electric dipole that enables the electrostatic control of its flow, and optical dipole that is spatially varying in the moiré landscape. We show the hybridization of moiré interlayer exciton with photons in a planar 2D cavity leads to two types of moiré polaritons that exhibit distinct forms of topological transport phenomena including the spin/valley Hall and polarization Hall effects, which feature remarkable electrical tunability through the control of exciton-cavity detuning by the interlayer bias.

Direct measurement of the intrinsic electric dipole moment in pear-shaped thorium-228

It is now well established that atomic nuclei composed of certain combinations of protons and neutrons can adopt reflection-asymmetric, or octupole-deformed, shapes at low excitation energy. These nuclei show promise in the search for a permanent atomic electric dipole moment, the existence of which has implications for physics beyond the Standard Model. Theoretical studies have suggested that certain isotopes of thorium may have the largest octupole deformation. However, due to experimental challenges, the extent of the octupole collectivity in the low-energy states in these thorium nuclei has not yet been demonstrated. This paper reports measurements of the lifetimes of low-energy states in 228Th (Z = 90) undertaken using the mirror symmetric centroid difference method, which is a direct electronic fast-timing technique. Lifetime measurements of the low-lying Jp = 1- and 3- states, which are the first for a thorium isotope, have allowed the B(E1) rates and the intrinsic dipole moment to be determined. The results are in agreement with those of previous theoretical calculations allowing the extent of the octupole deformation of 228Th to be estimated. This study indicates that the nuclei 229Th and 229Pa (Z = 91) may be good candidates for the search for a permanent atomic electric dipole moment.

Significance of Non-Linear Terms in the Relativistic Coupled-Cluster Theory in the Determination of Molecular Properties

The relativistic coupled-cluster (RCC) theory has been applied recently to a number of heavy molecules to determine their properties very accurately. Since it demands large computational resources, the method is often approximated to single and double excitations (RCCSD method). The effective electric fields ( E e f f ) and molecular permanent electric dipole moments (PDMs) of SrF, BaF, and mercury monohalides (HgX with X = F, Cl, Br, and I) molecules are of immense interest for probing fundamental physics. In our earlier calculations of E e f f and PDMs for the above molecules, we neglected the non-linear terms in the property evaluation expression of the RCCSD method. In this work, we demonstrate the roles of these terms in determining the above quantities and their computational time scalability with the number of processors of a computer. We also compare our results with previous calculations that employed variants of RCC theory, as well as other many-body methods and available experimental values.

CP -violating dark photon interaction

We introduce a scenario for CP-violating (CPV) dark photon interactions in the context of non-abelian kinetic mixing. Assuming an effective field theory that extends the Standard Model (SM) field content with an additional $U(1)$ gauge boson ($X$) and a $SU(2)_L$ triplet scalar, we show that there exist both CP-conserving and CPV dimension five operators involving these new degrees of freedom and the SM $SU(2)_L$ gauge bosons. The former yields kinetic mixing between the $X$ and the neutral $SU(2)_L$ gauge boson (yielding the dark photon), while the latter induces CPV interactions of the dark photon with the SM particles. We discuss experimental probes of these interactions using searches for permanent electric dipole moments (EDMs) and di-jet correlations in high-energy $pp$ collisions. It is found that the experimental limit on the electron EDM currently gives the strongest restriction on the CPV interaction. In principle, high energy $pp$ collisions provide a complementary probe through azimuthal angular correlations of the two forward tagging jets in vector boson fusion. In practice, observation of the associated CPV asymmetry is likely to be challenging.

The Stark Effect, Zeeman Effect, and Transition Dipole Moments for the B2Σ+−X2Σ+ Band of Aluminum Monoxide, AlO

Abstract The experimentally measured radiative lifetimes and branching ratios were combined to determine the transition dipole moments for the B 2Σ+(v = 0–3) → X 2Σ+(v = 0–6) bands of aluminum monoxide, AlO, and compared with theoretical predictions. The B 2Σ+–X 2Σ+ (0, 1) band of a molecular beam sample of AlO was recorded at high spectral resolution both field-free and in the presence of static electric and magnetic fields. The 27Al(I = 5/2) hyperfine interaction in the B 2Σ+(v = 0) state was analyzed. The observed Stark shifts were analyzed to produce permanent electric dipole moments of 1.94(8) D and 4.45(3) D for the B 2Σ+(v = 0) and X 2Σ+(v = 1) states, respectively. It is demonstrated that the observed Zeeman spectra can be simulated using an effective Hamiltonian with the associated expected g-factors for both the X 2Σ+(v = 1) and B 2Σ+(v = 0) states.

Absolute pressure and gas species identification with an optically levitated rotor

The authors describe a novel variety of spinning-rotor vacuum gauge in which the rotor is a ∼4.7−μm−diameter silica microsphere, optically levitated. A rotating electrostatic field is used to apply torque to the permanent electric dipole moment of the silica microsphere and control its rotational degrees of freedom. When released from a driving field, the microsphere’s angular velocity decays exponentially with a damping time inversely proportional to the residual gas pressure and dependent on gas composition. The gauge is calibrated by measuring the rotor mass with electrostatic co-levitation and assuming a spherical shape, confirmed separately, and uniform density. The gauge is cross-checked against a capacitance manometer by observing the torsional drag due to a number of different gas species. The techniques presented can be used to perform absolute vacuum measurements localized in space, owing to the small dimensions of the microsphere and the ability to translate the optical trap in three dimensions, as well as measurements in magnetic field environments. In addition, the dynamics of the microsphere, paired with a calibrated vacuum gauge, can be used to measure the effective molecular mass of a gas mixture without the need for ionization and at pressures up to approximately 1 mbar.

Guiding neutral polar molecules by electromagnetic vortex field

ABSTRACT It is shown, within classical mechanics, that the field of an electromagnetic vortex is capable of capturing and guiding neutral molecules endowed with a permanent electric dipole moment (PEDM). Similarly as in the case of the magnetic field applied to elementary particles or atoms, this effect turns out to be very delicate because of the small values of PEDM observed in real molecules. They amount to (electron charge × fermi) or less, which requires the use of very strong electric fields (reaching ). It has also been observed that there exists a threshold in field strength above which the particles are ejected from the trap. Trajectories of guided particles are usually quite chaotic, which is a consequence of non-linearity of the equations of motion. With a very special and precise adjustment of parameters, a regular (i.e. circular, in the transverse plane) trajectory can be obtained. The presence of an additional constant electric field pointing along the direction of the wave propagation might help to achieve the necessary tuning and realize such trajectories.

Comment on: “Bidimensional bound states for charged polar nanoparticles”

In a recent paper Castellanos-Jaramillo and Castellanos-Moreno proposed a simple quantum-mechanical model for an electron in the vicinity of an ionized nanostructure with a permanent electric dipole. They chose the interaction of the electron with the charge and the dipole in such a way that the resulting Schr\"{o}dinger equation is separable into radial and angular parts. In this comment we show that those authors did not solve the angular eigenvalue equation with proper periodic boundary conditions and that they also made a mistake in the elimination of the first derivative in the radial equation. Such errors invalidate their results of the Einstein coefficients for the $\left( GaAs\right)_{3}$ system considered.

Search for electric dipole moments

Searches for permanent electric dipole moments of fundamental particles and systems with spin are the experiments most sensitive to new CP violating physics and a top priority of a growing international community. We briefly review the current status of the field emphasizing on the charged leptons and lightest baryons.

Field-free, Stark, and Zeeman spectroscopy of the Ã2Π1/2−X̃2Σ+ transition of ytterbium monohydroxide

The 000A2Π1/2−X2Σ+, 110A2Π1/2−X2Σ+, and 101A2Π1/2−X2Σ+ bands of an internally cold molecular beam sample of ytterbium monohydroxide, YbOH, have been recorded at the near natural linewidth limit and analyzed to determine the fine structure parameters. Numerous lines in the 000A2Π1/2−X2Σ+ band associated with the lowest rotational levels were recorded in the presence of a static electric field and analyzed to determine the magnitude of the molecular frame permanent electric dipole moment, |μel|, for the X2Σ+(0,0,0) and A2Π1/2(0,0,0) states of 1.9(2) and 0.43(10) D, respectively. An electrostatic polarizability model is used to predict the μel for the X2Σ+(0,0,0) state. The 000A2Π1/2−X2Σ+ band is recorded in the presence of a weak static magnetic field to observe the electric dipole allowed transitions having ΔJ=−2, which are used to assist in the rotational quantum number assignment and confirm the identity of the excited state. An expression for the A2Π1/2(0,0,0) magnetic g factor is derived and shown to correctly model the observed magnetic tuning. A comparison with YbF is made and implications for the use of YbOH as a venue for symmetry violation measurements are discussed.

Quasi-one-dimensional approximation for Bose–Einstein condensates transversely trapped by a funnel potential

Starting from the standard three-dimensional (3D) Gross–Pitaevskii equation (GPE) and using a variational approximation, we derive an effective one-dimensional nonpolynomial Schrödinger equation (1D-NPSE) governing the axial dynamics of atomic Bose–Einstein condensates (BECs) under the action of a singular but physically relevant funnel-shaped transverse trap, i.e. an attractive 2D potential ∼−1/r (where r is the radial coordinate in the transverse plane), in combination with the repulsive self-interaction. Wave functions of the trapped BEC are regular, in spite of the potential’s singularity. The model applies to a condensate of particles (small molecules) carrying a permanent electric dipole moment in the field of a uniformly charged axial thread, as well as to a quantum gas of magnetic atoms pulled by an axial electric current. By means of numerical simulations, we verify that the effective 1D-NPSE provides accurate static and dynamical results, in comparison to the full 3D GPE, for both repulsive and attractive signs of the intrinsic nonlinearity.

Lifetime measurements of the A 2Π1/2 and A 2Π3/2 states in BaF

Time resolved detection of laser induced fluorescence from pulsed excitation of electronic states in barium monofluoride (BaF) molecules has been performed in order to determine the lifetimes of the $A^2\Pi_{1/2}$ and $A^2\Pi_{3/2}$ states. The method permits control over experimental parameters such that systematic biases in the interpretation of the data can be controlled to below $10^{-3}$ relative accuracy. The statistically limited values for the lifetimes of the $A^2\Pi_{1/2}(\nu=0)$ and $A^2\Pi_{3/2}(\nu=0)$ states are 57.1(3) ns and 47.9(7)~ns, respectively. The ratio of these values is in good agreement with scaling for the different excitation energies. The investigated molecular states are of relevance for an experimental search for a permanent electric dipole moment (EDM) of the electron in BaF.

Effect of Chemical Order in the Structural Stability and Physicochemical Properties of B12N12 Fullerenes

The effect of chemical order in the structural and physicochemical properties of B12N12 [4,6]-fullerene (BNF) isomers was evaluated using density functional theory and molecular dynamic calculations. The feasibility to find stable BNF isomers with atomic arrangement other than the well-known octahedral Th-symmetry was explored. In this study, the number of homonuclear bonds in the modeled nanostructures was used as categorical parameter to describe and quantify the degree of structural order. The BNF without homonuclear bonds was identified as the most energetically favorable isomer. However, a variety of BNF arrays departing from Th-symmetry was determined as stable structures also. The calculated vibrational spectra suggest that isomers with chemical disorder can be identified by infrared spectroscopy. In general, formation of homonuclear bonds is possible meanwhile the entropy of the system increases, but at expense of cohesive energy. It is proposed that formation of phase-segregated regions stablishes an apparent limit to the number of homonuclear bonds in stable B12N12 fullerenes. It was found that formation of homonuclear bonds decreases substantially the chemical hardness of BNF isomers and generates zones with large charge density, which might act as reactive sites. Moreover, chemical disorder endows BNF isomers with a permanent electric dipole moment as large as 3.28 D. The obtained results suggest that by manipulating their chemical order, the interaction of BNF’s with other molecular entities can be controlled, making them potential candidates for drug delivery, catalysis and sensing.

Electronic Structure and Bonding of the Fastidious Species CN2 and CP2: A First-Principles Study.

The transient molecular species CN2 (CNN, NCN, c(yclic)-CN2) and CP2 (CPP, PCP, c(yclic)-CP2), along with the isoelectronic to CNN and isovalent to CPP, CCO, have been studied theoretically through the ab initio methodologies multireference configuration interaction (MRCI) and RCCSD(T) coupled with augmented correlation-consistent quintuple and sextuple basis sets. For the CNN, NCN, and c-CN2 molecules, the examined states are [X̃3Σ-, ã1Δ, b̃1Σ+, Ã3Π, and c̃1Π], X̃3Σg-, and X̃1A1, respectively. The analogous phosphorous system CPP has been studied theoretically for the first time. Our results show that the symmetries 3Σ-, 1Δ, and 1Σ+ are not stationary states; thence, the ground state of CPP is of 3Π symmetry and of similar electronic structure to that of the Ã3Π state of CNN. For most of the symmetries studied, we have constructed fully optimized potential energy profiles or "cuts" through the corresponding surfaces at the MRCI level of theory in an effort to follow the (valence) electronic distributions from the "selected" adiabatic species to equilibrium. Our numerical results are in excellent agreement with existing experimental data and previous, although limited, high-level ab initio calculations. Finally, it should be said that some of our findings like dissociation energies, permanent electric dipole moments, and bonding considerations are addressed for the first time.

Electro-optic sensor for static fields

A sensor has been developed for low frequency and DC electric fields E. The device is capable of measuring fields with varDelta mathrm{E}= 4 (1) V/cm resolution. It is based on a Y-cut Z-propagation lithium niobate electro-optic crystal. For a particular commercially available bare crystal, we achieved an in air time constant tau _mathrm{c}(mathrm air)= 6.4(1.8) h for the decay of the electro-optic signal. This enables field monitoring for several hours. As an application, we demonstrated that a constant electric field E^{mathrm{ext}} = 640 V/cm applied via external electrodes to a particular spherical glass container holding an Xe/He gas mixture decays inside this cell with a time constant tau _{E}^{mathrm{glass}} = 2.5(5) h. This is sufficient for the needs of experiments searching for a permanent electric dipole moment in ^{129}Xe. An integrated electric field sensor has been constructed which is coupled to a light source and light detectors via optical fibers. The sensor head does not contain any electrically conducting material.

Solute-solvent electronic interaction is responsible for initial charge separation in ruthenium complexes [Ru(bpy)3]2+ and [Ru(phen)3]2+

Origin of the initial charge separation in optically-excited Ruthenium(II) tris(bidentate) complexes of intrinsic D3 symmetry has remained a disputed issue for decades. Here we measure the femtosecond two-photon absorption (2PA) cross section spectra of [Ru(2,2′-bipyridine)3]2 and [Ru(1,10-phenanthroline)3]2 in a series of solvents with varying polarity and show that for vertical transitions to the lower-energy 1MLCT excited state, the permanent electric dipole moment change is nearly solvent-independent, Δμ = 5.1–6.3 D and 5.3–5.9 D, respectively. Comparison of experimental results with quantum-chemical calculations of complexes in the gas phase, in a polarizable dielectric continuum and in solute-solvent clusters containing up to 18 explicit solvent molecules indicate that the non-vanishing permanent dipole moment change in the nominally double-degenerate E-symmetry state is caused by the solute-solvent interaction twisting the two constituent dipoles out of their original opposite orientation, with average angles matching the experimental two-photon polarization ratio.

Room-Temperature Giant Stark Effect of Single Photon Emitter in van der Waals Material.

Single photon emitters (SPEs) are critical building blocks needed for quantum science and technology. For practical applications, room-temperature solid-state platforms are critically demanded. To scale up quantum information processing using, for example, wavelength division multiplexing quantum key distribution, a large tuning range beyond emission line width of single photon energy is required. Stark effect can tune the single photon energy by an electric field. However, it has been achieved only at cryogenic temperature to pursue a shift larger than emission line width. A large Stark tuning beyond emission line width at room temperature still remains elusive. Here we report the first room-temperature Stark effect of SPEs with a giant Stark shift of single photon energy up to 43 meV/(V/nm), largest among all previous color center emitters. Such a giant Stark shift is 4-fold larger than its line width at room temperature, demonstrated by exploiting hBN color centers. Moreover, the intrinsic broken symmetries are determined via angle-resolved Stark effect, for the first time, by the orientation of the electric permanent dipole moment in the solid-state SPE, which is unachievable in traditional optical polarization measurement. The remarkable Stark shift discovered here and the significant advance in understanding its atomic structure pave a way toward the scalable solid-state on-chip quantum communication and computation at room temperature.

Ab initio calculations of the lowest 262s+1Λ± electronic states of 90ZrS including spin-orbit coupling

The electronic structure in the representation2S + 1Λ± of the diatomic molecule 90ZrS is carried out using (CASSCF/MRCI- single and double excitation)) ab-initio methods. In this work, 14 singlet and 12 triplet electronic states of energies below 36,000 cm−1, of which 8 singlet and 6 triplet excited states yet unobserved experimentally, are predicted.The potential energy curves (PECs) of these states are also computed in an interval of internuclear distances from about 1.5 Å to 4.0 Å. The spectroscopic constants ωe and ωeχe, the internuclear distance Re and the energy at equilibrium Te of the singlet and triplet states referred to the ground state energy at equilibrium are calculated and compared with previous experimental and theoretical results. The permanent electric dipole moments for these states are calculated for R around the equilibrium internuclear distances. The allowed transition dipole moments (TDM) between the calculated singlet and triplet states of 90ZrS molecule are also displayed.As a result of the spin orbit coupling (SOC) calculations, 52 electronic Ω(±) components generated in almost from the 26 states 2S + 1Λ± are obtained. This work has determined that the ground state is (X)1Σ+ with an equilibrium internuclear distance Re = 2.15 Å. However, the (1)3Δ1 is found very close to (X)1Σ+ situated 180 cm−1 above it, with an internuclear distance Re = 2.19 Å and becomes the lowest state after Re = 2.21 Å.

Cavity-control of interlayer excitons in van der Waals heterostructures

Monolayer transition metal dichalcogenides integrated in optical microcavities host exciton-polaritons as a hallmark of the strong light-matter coupling regime. Analogous concepts for hybrid light-matter systems employing spatially indirect excitons with a permanent electric dipole moment in heterobilayer crystals promise realizations of exciton-polariton gases and condensates with inherent dipolar interactions. Here, we implement cavity-control of interlayer excitons in vertical MoSe2-WSe2 heterostructures. Our experiments demonstrate the Purcell effect for heterobilayer emission in cavity-modified photonic environments, and quantify the light-matter coupling strength of interlayer excitons. The results will facilitate further developments of dipolar exciton-polariton gases and condensates in hybrid cavity – van der Waals heterostructure systems.