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Ring-shaped traveling wave Zeeman decelerator for both light and heavy molecules

Yabing Ji, Qing Liu, Yang Liu, Tao Yang, Shunyong Hou, Jianying Yin

Published Jan 30, 2023• 0 citations
Publisher

Abstract

Abstract Taming more species of molecules with large density is a long-standing goal in molecular science. Heavy molecule (> 100 amu) is of particular interest for precision measurements. However, decelerating a fast-moving beam of heavy molecules to rest remains challenging for Zeeman deceleration. Additionally, the traditional approach of pulsed Zeeman decelerator suffers from serious molecular loss during deceleration, significantly limiting its potential applications. Herein, we present a ring-shaped traveling wave Zeeman decelerator (RTWZD) featured with true three-dimensional smoothly-moving magnetic potential wells that directly solve the above intractable problems. With this approach, not only the density of the molecule can be greatly increased but also the range of molecular species for Zeeman deceleration can be extended from light to heavy. The performance of the RTWZD is characterized with both the theoretical analysis and the numerical calculation, where a group of atoms and molecules such as 7Li, 32O2, 88Sr19F and 174Yb19F are employed as testers. Losses in the traditional Zeeman decelerator can be avoided, yielding more than two orders of magnitude improvement in molecular density. These characteristics of the RTWZD make it an ideal toolbox to produce cold and dense atomic/molecular samples, enabling promising prospects for cold collision, sympathetic cooling, and precision measurement.

DOI
10.21203/rs.3.rs-2507806/v1

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Taming a broader range of molecular species with large density has been a long-standing goal in molecular science. Heavy molecules with masses greater than 100 amu are of particular interest for precision measurements. However, decelerating a fast-moving beam of such heavy molecules to rest remains challenging for Zeeman deceleration. Moreover, the traditional approach of pulsed Zeeman decelerator suffers from serious molecular loss during deceleration, significantly limiting its potential applications. Herein, we present a proposal of ring-shaped traveling wave Zeeman decelerator (RTWZD) featured with true three-dimensional smoothly moving magnetic potential wells that effectively solve the above intractable problems. With the RTWZD approach, not only can the density of the molecule be greatly increased but also the range of molecular species for Zeeman deceleration can be extended from light to heavy. The performances of the RTWZD are characterized by theoretical analysis and numerical simulations, utilizing a group of atoms and molecules such as $^{7}\mathrm{Li}, ^{16}\mathrm{O}_{2}, ^{88}\mathrm{Sr}^{19}\mathrm{F}$, and $^{174}\mathrm{Yb}^{19}\mathrm{F}$ as testers. Notably, losses encountered in the traditional Zeeman decelerator can be avoided, yielding more than two orders of magnitude improvement in molecular density. These characteristics of the RTWZD make it an ideal toolbox to produce cold and dense atomic/molecular samples, with promising prospects for cold collision, sympathetic cooling, and precision measurement.

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Improving the number and number density of cold molecules is a longstanding goal in cold molecule research. Stark deceleration provides an important access to taming polar molecules and makes the collision and high-resolution spectroscopy a reality. However, the full deceleration efficiency of the traditional Stark decelerator has been impeded by its intrinsic loss mechanisms, which significantly limit its applications. In this paper, we introduce an interspersed guiding deceleration strategy that surpasses the periodic phase stability limitations of traditional Stark decelerator. Our approach is theoretically and experimentally validated using the $\mathrm{N}{\mathrm{D}}_{3}$ molecule, achieving significant gains of $3\ensuremath{\sim}8$ for all final velocity ranges. Additionally, our method requires a lower operation number of switching that is beneficial for reducing the consumption of the high-voltage switches and suitable for controlling a large number of deceleration stages. This method is applicable to any traditional crossed-pin Stark decelerator and can stop a wider variety of molecular species with higher densities, including those with a small Stark shift-to-mass ratio. It is anticipated to become an essential tool for producing cold and dense molecular samples, offering promising prospects for cold collision studies and precision measurements.

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Abstract Taming more species of molecules with large density is a long-standing goal in molecular science. Heavy molecule (> 100 amu) is of particular interest for precision measurements. However, decelerating a fast-moving beam of heavy molecules to rest remains challenging for Zeeman deceleration. Additionally, the traditional approach of pulsed Zeeman decelerator suffers from serious molecular loss during deceleration, significantly limiting its potential applications. Herein, we present a ring-shaped traveling wave Zeeman decelerator (RTWZD) featured with true three-dimensional smoothly-moving magnetic potential wells that directly solve the above intractable problems. With this approach, not only the density of the molecule can be greatly increased but also the range of molecular species for Zeeman deceleration can be extended from light to heavy. The performance of the RTWZD is characterized with both the theoretical analysis and the numerical calculation, where a group of atoms and molecules such as 7Li, 32O2, 88Sr19F and 174Yb19F are employed as testers. Losses in the traditional Zeeman decelerator can be avoided, yielding more than two orders of magnitude improvement in molecular density. These characteristics of the RTWZD make it an ideal toolbox to produce cold and dense atomic/molecular samples, enabling promising prospects for cold collision, sympathetic cooling, and precision measurement.
Taming a broader range of molecular species with large density has been a long-standing goal in molecular science. Heavy molecules with masses greater than 100 amu are of particular interest for precision measurements. However, decelerating a fast-moving beam of such heavy molecules to rest remains challenging for Zeeman deceleration. Moreover, the traditional approach of pulsed Zeeman decelerator suffers from serious molecular loss during deceleration, significantly limiting its potential applications. Herein, we present a proposal of ring-shaped traveling wave Zeeman decelerator (RTWZD) featured with true three-dimensional smoothly moving magnetic potential wells that effectively solve the above intractable problems. With the RTWZD approach, not only can the density of the molecule be greatly increased but also the range of molecular species for Zeeman deceleration can be extended from light to heavy. The performances of the RTWZD are characterized by theoretical analysis and numerical simulations, utilizing a group of atoms and molecules such as 7Li,16O2,88Sr19F^{7}\mathrm{Li}, ^{16}\mathrm{O}_{2}, ^{88}\mathrm{Sr}^{19}\mathrm{F}7Li,16O2​,88Sr19F, and 174Yb19F^{174}\mathrm{Yb}^{19}\mathrm{F}174Yb19F as testers. Notably, losses encountered in the traditional Zeeman decelerator can be avoided, yielding more than two orders of magnitude improvement in molecular density. These characteristics of the RTWZD make it an ideal toolbox to produce cold and dense atomic/molecular samples, with promising prospects for cold collision, sympathetic cooling, and precision measurement.
Abstract There is increasing interest in cold heavy polar molecular species for their applications in fundamental physics, such as the tests of the electron’s electric dipole moment. Here we propose a switched ring Stark decelerator suitable for slowing both light and heavy polar molecules. Two typical polar molecular species, ND 3 and 205 TlF, are employed to test the feasibility of our scheme with the help of trajectory calculation. Our proposed scheme is found to share many advantages with the state-of-the-art traveling wave decelerator, yet with relatively simple electronics and flexible operation modes. Sub-millikelvin molecular samples can be conveniently obtained in our decelerator using a combined operation mode. These monochromatic beams are ideal starting points for precise studies of molecular collision, cold chemistry and high-resolution spectroscopy.
Abstract Molecular synchrotrons offer a promising platform for molecular beam collision studies with enhanced collision sensitivity. However, existing synchrotron designs suffer from constraints in velocity range, particle mass, and molecular flux. Here, we propose a novel magnetic synchrotron consisting of 1048 coils arranged in a nearly perfect circular ring, which generates a series of deep (~2.2 T), moving three-dimensional traps. Its key advantages are as follows: I) It enables direct loading of supersonic light species (400 m/s for NH) from a pulsed valve, thereby circumventing the flux limitations of upstream decelerators and significantly increasing the number of captured molecules. II) It is capable of confining heavy paramagnetic molecules (e.g., YO) at the modest injection velocities (tens of meters per second) typical of buffer-gas cooling. III) The high symmetry of the structure eliminates stop-bands, allowing paramagnetic molecules to be confined over a continuously tunable velocity range and achieving a long storage lifetime (~1.5 s for NH). This synchrotron design overcomes major limitations of previous devices and opens new possibilities for high-sensitivity collision studies and quantum-state-resolved chemistry. Moreover, by straightening the ring, the structure can function as a Zeeman decelerator, which is predicted to surpass recent deceleration schemes (Y. Ji et al., Phys. Rev. A 108, 043115, 2023) in efficiency by several times for both light and heavy molecules.
The growing field of cold molecule physics has demonstrated many methods of quantum control for precision measurement and molecular interaction studies. One particular method is Stark deceleration, which uses electric field gradients to produce packets of slow polar molecules. Since Stark deceleration does not increase phase-space density, the efficiency of the deceleration process is critical in determining the final cold molecule density. This dissertation describes three different Stark deceleration techniques. The first type of deceleration is pulsed-pin deceleration. We use this technique to produce slow OH molecules that can be trapped for cold collision studies. A two photon state-selective detection system, which includes a 118 nm photon, is used to determine the density distribution of OH in the trap. We explore the advantages and limitations to creating 118 nm light. The second and third types of Stark deceleration are pulsed-ring and traveling-wave methods of running a ring-geometry decelerator. Ring-geometry decelerators present improved deceleration efficiencies due to the cylindrical symmetry of the electrodes and true three-dimensional confinement. The pulsed-ring mode of the ring decelerator uses commercial high-voltage switches to apply discrete pulses to the ring electrodes. The continuous operation mode of the ring decelerator uses varying sine-wave voltages to create a traveling Stark potential well and has proven to be incredibly challenging due to the analog high voltage requirements of the system. In order to bring ND3 seeded in krypton (∼415 m/s) down to rest in the laboratory, sine wave voltages with amplitudes up to ±10 kV, currents up to 500 mA, and a bandwidth of 30 kHz down to DC are required. We describe a high-voltage amplifier that can be used for traveling-wave deceleration. The traveling-wave Stark deceleration mode is then compared to the pulsed-ring Stark deceleration mode and cases where one mode is superior to another are discussed.
The design of a modular moving trap Zeeman decelerator capable of decelerating gas pulses produced from a supersonic source is presented here. Unlike the conventional form of Zeeman decelerator, paramagnetic particles are confined in a 3D potential throughout the deceleration process. The decelerator field is produced by flattened helical coils and currents of up to 1000 A peak. As the coils are periodic in nature, each coil produces a number of deep, quadrupole traps along the molecular beam axis. The resultant periodic field is described as a travelling wave. The application of the appropriate time dependent current allows the traps to move through the four coil modules. In order to compensate for the weaker transverse confinement, a quadrupole guide, operating at 700 A DC, is required to prevent further losses during the deceleration process. The operation of the decelerator relies on the power electronics developed specifically for the quadrupole and the decelerator coils. Due to the electromagnetic interference generated through the switching of the large currents, much of the electronics used to control the power electronics had to be developed specifically. The quadrupole power electronics have been designed to produce fast switching edges. This is necessary to minimise the interaction of the particles within the fringe field regions while maximising the interaction time within the pure quadrupole field. Even at a modest voltage applied to the circuitry, the rise time in current to 700 A has been reduced by a half. The decelerator power electronics must be capable of producing an alternating waveform with an amplitude of at least 500 A for each of the coil phases. Furthermore, the frequency of the waveforms must be tunable within a range of 10 kHz to 0 Hz. Through a combination of pulse width modulation and knowledge of the electrical properties of the coil it is possible to synthesise an alternating current waveform from a 800 V DC supply using a suitable switching circuit. %The challenge of switching such high powers is the transient voltage spikes that can be produced, however, these can be avoided through careful consideration of the layout of the circuit. Decelerators such as this do not cool the sample but instead reduces the mean velocity of a subset of particles which remained trapped. This maintains the phase space density of trapped particles. Modelling the magnetic fields generated by the decelerator coils has been necessary in order to understand the phase space acceptance of the decelerator. The helical nature of the coils required the development of a specific algorithm in order to calculate the field generated by each wire element. The resultant potential can then be interpolated using a tricubic interpolator to extract the field gradients necessary for numerical simulations of the particle trajectories. Including the effects of the pulse width modulated on the trap facilitates the characterisation of the acceptance of the decelerator and the limitations of the current iteration of the design. The numerical simulations can also be compared to experimental results gathered for metastable argon. The 3D guiding, or velocity bunching, of the gas packet over a range of velocities has been demonstrated. The ability to 3D guide and decelerate were severely hampered by the failure of key electronic components, limiting three coils to 100 A peak, moreover, these traps were sub-optimally loaded. Deceleration from 350 to 347 m/s and 342 to 310 m/s has been observed. The design of a trap capable of simultaneously loading samples of decelerated CaH and Li while allowing the cooling of Li would potentially allow for the sympathetic cooling of a molecular species with an atomic refrigerant. This particular atom-molecule system would also facilitate the examination of controlled chemistry and collisions over a range of temperatures through state selection of the reactants. The loading of the trap has been optimised in 1D for CaH with a loading efficiency of 52.2 % while only 7.3 % of Li is loaded when each of the gas packets has a mean velocity of 11 m/s. This implies that the source of the Li must be at least 130 times brighter than that of the CaH.
Improving the number and number density of cold molecules is a longstanding goal in cold molecule research. Stark deceleration provides an important access to taming polar molecules and makes the collision and high-resolution spectroscopy a reality. However, the full deceleration efficiency of the traditional Stark decelerator has been impeded by its intrinsic loss mechanisms, which significantly limit its applications. In this paper, we introduce an interspersed guiding deceleration strategy that surpasses the periodic phase stability limitations of traditional Stark decelerator. Our approach is theoretically and experimentally validated using the ND3\mathrm{N}{\mathrm{D}}_{3}ND3​ molecule, achieving significant gains of $3\ensuremath{\sim}8$ for all final velocity ranges. Additionally, our method requires a lower operation number of switching that is beneficial for reducing the consumption of the high-voltage switches and suitable for controlling a large number of deceleration stages. This method is applicable to any traditional crossed-pin Stark decelerator and can stop a wider variety of molecular species with higher densities, including those with a small Stark shift-to-mass ratio. It is anticipated to become an essential tool for producing cold and dense molecular samples, offering promising prospects for cold collision studies and precision measurements.