Optica Applicata

From molecular spectroscopy to entanglement of atoms - a trek with supersonic velocity

J. Koperski

Published Jan 1, 2012• 0 citations

Abstract

The supersonic free-jet expansion technique is being used in different fields of research in physics, and physical chemistry to study vibrational and rotational molecular structures in ground and excited electronic energy states. The supersonic beam technique exploits a source of monokinetic, rotationally and vibrationally cold van der Waals (vdW) molecules that are very weakly bound in their ground electronic states. In this article we review experiments at the Jagiellonian University in Kraków (Poland) in which the supersonic free-jet beam serves as a source of ground-state vdW molecules in studies of neutral-neutral interactions between 12-group metal (Me = Zn, Cd, Hg) and 18-group noble gas (Ng = He, Ne, Ar, Kr, Xe) atoms. The experiments lead to determination of spectroscopical characteristics and interatomic potentials of MeNg and Me2 molecules, allowing determination of distinct trends in the Me-Ng and Me-Me interactions in different regions of internuclear separation. The determined interatomic potentials are also used in designing mechanisms of internal vibrational cooling of molecules photoassociated in magneto-optical traps. Recently, versatility of supersonic beams is confirmed in quantum information where the technique is planned to be used to create pairs of entangled atoms in experiments dedicated for testing of Bell’s inequality for atoms. A purpose of the experiment - which is in a preparational stage in our laboratory - is to create pairs of entangled cadmium atoms with regard to their nuclear spin orientations. It is planned to be achieved in supersonic molecular beams of cadmium dimers using two dye-laser pulses and stimulated Raman process leading to a controlled photodissociation of the molecule.

DOI: 10.5277/oa120219

Related papers

Molecules in the cold environment of a supersonic free-jet beam: from spectroscopy of neutral–neutral interactions to a test of Bell's inequality

J. Koperski, Edward S. Fry

The supersonic free-jet expansion technique has been used in different fields of research in physics, physical chemistry and chemistry to study vibrational and rotational molecular structures in ground and excited electronic energy states as well as in cold chemistry to study chemical reactions in a unique environment. The supersonic beam technique, as a widely used method in laser spectroscopy of molecules, exploits a source of monokinetic, rotationally and vibrationally cold molecules, that are very weakly bound in their ground electronic states (van der Waals molecules). In experiments at Jagiellonian University the supersonic free-jet beam serves as a source of ground-state van der Waals objects in studies of neutral–neutral interactions between group 12 metal (M = Zn, Cd, Hg) and noble gas (NG) atoms. Recently, the method has been applied as a source of entangled 199 Hg atom pairs in order to test Bell's inequality in an experiment at Texas A&M University.

Journal of Physics B Atomic Molecular and Optical PhysicsSep 25, 200619 citations

Optical Stark deceleration of neutral molecules from supersonic expansion with a rotating laser beam

Yongcheng Yang, Shunyong Hou, Lianzhong Deng

Cold molecules have great scientific significance in high-resolution spectroscopy, precision measurement of physical constants, cold collision, and cold chemistry. Supersonic expansion is a conventional and versatile method to produce cold molecules with high kinetic energies. We theoretically show here that fast-moving molecules from supersonic expansion can be effectively decelerated to any desired velocity with a rotating laser beam. The orbiting focus spot of the red-detuned laser serves as a two-dimensional potential well for the molecules. We analyze the dynamics of the molecules inside the decelerating potential well and investigate the dependence of their phase acceptance by the potential well on the tilting angle of the laser beam. ND 3 molecules are used in the test of the scheme and their trajectories under the impact of the decelerating potential well are numerically simulated using the Monte Carlo method. For instance, with a laser beam of 20 kW in power focused into a pot of in waist radius, ND 3 molecules of 250 m/s can be brought to a standstill by the decelerating potential well within a time interval of about 0.73 ms. The total angle covered by the rotating laser beam is about 5.24° with the distance travelled by the potential well being about 9.13 cm. In fact, the molecules can be decelerated to any desired velocity depending on the parameters adopted. This scheme is simple in structure and easy to be realized in experiment. In addition, it is applicable to decelerating both molecules and atoms.

Chinese Physics BMay 1, 20184 citations

Ultracold ground-state KCs molecules

Krzysztof P. Zamarski

Ultracold atomic gases have proven to be a versatile tool for the study of many-body quantum physics thanks to the high degree of control that they offer. However, interactions between neutral atoms are usually short-ranged and isotropic, which limits their applicability as a simulator of real condensed matter systems. One of the most common methods of introducing stronger interactions into an ultracold gas is associating pairs of atoms of two different elements into molecules. Such molecules possess a body-fixed electric dipole moment, which can be addressed by an external electric field or microwave radiation to engineer long-ranged, tunable dipolar interactions. In addition to constituting an analogue quantum simulator, ultracold dipolar molecules show potential as a platform for digital quantum computation, precision measurements, and the study of quantum chemistry. The main result presented in this thesis is the first successful synthesis of ultracold 39K133Cs molecules in their vibrational and rotational ground state. Using a novel simultaneous cooling scheme for potassium and caesium, our team has been able to produce mixtures that are cold enough for efficient magnetoassociation into weakly bound molecules to take place. By performing high-resolution laser spectroscopy of these molecules, I have identified a two-photon pathway to the ground state via an exceptionally narrow intermediate excited state. I was then able to perform Stimulated Raman Adiabatic Passage (STIRAP) along that pathway with one-way efficiencies up to 71%, producing trapped samples of up to 3500 ground-state molecules at temperatures of 1 µK. The lifetime of these samples is currently limited by a near-universal two-body loss process, a further study of which could shed light on similar loss mechanisms in other molecular species. I have also carried out preliminary rotational spectroscopy, which paves the way towards using KCs molecules as a controlled interacting spin system and a refinement of their hyperfine coupling constants. The thesis ends with a detailed outline of further steps that should be taken to improve the efficiency of STIRAP, as well as the population and coherence lifetimes in KCs samples. It is followed by a list of suggested experiments that could be carried out using our system after it undergoes the described technical upgrades. Some of these experiments are directly inspired by the results I have obtained during my six-month research stay in the KRb laboratory at JILA.

Jan 1, 20260 citations

Harnessing the Power of Adiabatic Curve Crossing to Populate the Highly Vibrationally Excited H 2 ( v = 7 , j = 0 ) Level

William E. Perreault, Haowen Zhou, Nandini Mukherjee +1 more

A large ensemble of ∼10^{9} H_{2} (v=7, j=0) molecules is prepared in the collision-free environment of a supersonic beam by transferring nearly the entire H_{2} (v=0, j=0) ground-state population, where v and j are the vibrational and rotational quantum numbers, respectively. This is accomplished by controlling the crossing of the optically dressed adiabatic states using a pair of phase coherent laser pulses. The preparation of highly vibrationally excited H_{2} molecules opens new opportunities to test fundamental physical principles using two loosely bound yet entangled H atoms.

Physical Review LettersApr 24, 202025 citations

High-temperature high-pressure all-metal pulsed source of van der Waals dimers: Towards the Einstein-Podolsky-Rosen experiment

Tomasz Urbańczyk, J. Koperski

An all-metal pulsed source of van der Waals (vdW) dimers was constructed; it operates at temperatures up to 1000 K and carrier gas stagnation pressures up to 10 bars. Performance of the source was demonstrated in the production and spectroscopy of both CdAr and Cd(2) molecules in a supersonic beam expansion. Simulation of the recorded laser induced fluorescence (LIF) excitation spectra using the B(3)1(5(3)P(1)) ← X(1)0(+)(5(1)S(0)) and b(3)0(u)(+)(5(3)P(1))←X(1)0(g)(+)(5(1)S(0)) transitions in CdAr and Cd(2), respectively, showed that these molecules were produced with a rotational temperature in the range from 3 K to 19 K. The source was incorporated into an experimental set-up dedicated to the realization of Bohm's spin-1/2 particle version of the Einstein-Podolsky-Rosen experiment for ((111)Cd)(2) molecules.

Review of Scientific InstrumentsAug 1, 201212 citations

Dynamical Spectroscopy of Transient He2 Molecules

Milou van Rijnbach

The velocities of atoms can be manipulated by near-resonant laser light. After many absorption-spontaneous emission cycles momentum is transferred to the atoms in the direction of the laser beam. In this way atoms can be slowed down and cooled to milliKelvin temperatures and below. In three mutually orthogonal pairs of counter-propagating laser beams in combination with a magnetic field atoms can be cooled and trapped. In this so-called magneto-optical trap (MOT) two atoms can be excited to a molecular state by absorption of a photon. This technique is called photoassociation spectroscopy. In our case we study metastable helium atoms, which have a large internal energy. When two metastable helium atoms approach each other, one of the atoms ionizes and the ions are detected by a microchannelplates detector. When a probe laser beam is directed onto the MOT cloud and scanned in frequency, atom pairs can be excited to several ro-vibrational states. In the excited state the metastable helium atoms are accelerated towards each other and ionize at short internuclear distance. The ro-vibrational states appear as peaks in the ionization signal and from the position of these states information on the excited state interaction potential can be extracted.

Jan 19, 20048 citations