24 results found
Alauze X, Lim J, Trigatzis MA, et al., 2021, An ultracold molecular beam for testing fundamental physics, Quantum Science and Technology, Vol: 6
We use two-dimensional transverse laser cooling to produce an ultracold beam of YbF molecules. Through experiments and numerical simulations, we study how the cooling is influenced by the polarization configuration, laser intensity, laser detuning and applied magnetic field. The ultracold part of the beam contains more than 2 105 molecules per shot and has a temperature below 200 μK, and the cooling yields a 300-fold increase in the brightness of the beam. The method can improve the precision of experiments that use molecules to test fundamental physics. In particular, the beam is suitable for measuring the electron electric dipole moment with a statistical precision better than 10-30 e cm.
Jurgilas S, Chakraborty A, Rich CJH, et al., 2021, Collisions between Ultracold Molecules and Atoms in a Magnetic Trap, PHYSICAL REVIEW LETTERS, Vol: 126, ISSN: 0031-9007
Fitch NJ, Lim J, Hinds EA, et al., 2021, Methods for measuring the electron's electric dipole moment using ultracold YbF molecules, QUANTUM SCIENCE AND TECHNOLOGY, Vol: 6, ISSN: 2058-9565
Ho C, Devlin JA, Rabey I, et al., 2020, New techniques for a measurement of the electron's electric dipole moment, New Journal of Physics, Vol: 22, ISSN: 1367-2630
The electric dipole moment of the electron (eEDM) can be measured with high precision using heavy polar molecules. In this paper, we report on a series of new techniques that have improved the statistical sensitivity of the YbF eEDM experiment. We increase the number of molecules participating in the experiment by an order of magnitude using a carefully designed optical pumping scheme. We also increase the detection efficiency of these molecules by another order of magnitude using an optical cycling scheme. In addition, we show how to destabilise dark states and reduce backgrounds that otherwise limit the efficiency of these techniques. Together, these improvements allow us to demonstrate a statistical sensitivity of 1.8 x 10⁻²⁸ e cm after one day of measurement, which is 1.2 times the shot-noise limit. The techniques presented here are applicable to other high-precision measurements using molecules.
Fitch NL, Parazzoli LP, Lewandowski HJ, 2020, Collisions between ultracold atoms and cold molecules in a dual electrostatic-magnetic trap, PHYSICAL REVIEW A, Vol: 101, ISSN: 2469-9926
Caldwell L, Williams H, Fitch N, et al., 2020, Long rotational coherence times of molecules in a magnetic trap, Physical Review Letters, Vol: 124, ISSN: 0031-9007
Polar molecules in superpositions of rotational states exhibit long-range dipolar interactions, but maintaining their coherence in a trapped sample is a challenge. We present calculations that show many laser-coolable molecules have convenient rotational transitions that are exceptionally insensitive to magnetic fi elds. We verify this experimentally for CaF where we find a transition with sensitivity below 5 HzG‾¹ and use it to demonstrate a rotational coherence time of 6.4(8) ms in a magnetic trap. Simulations suggest it is feasible to extend this to > 1 s using a smaller cloud in abiased magnetic trap.
Caldwell L, Devlin J, Williams H, et al., 2019, Deep Laser Cooling and Efficient Magnetic Compression of Molecules, Physical Review Letters, Vol: 123, ISSN: 0031-9007
We introduce a scheme for deep laser cooling of molecules based on robust dark states at zero velocity. By simulating this scheme, we show it to be a widely applicable method that can reach the recoil limit or below. We demonstrate and characterise the method experimentally, reachinga temperature of 5.4(7) μK. We solve a general problem of measuring low temperatures for large clouds by rotating the phase-space distribution and then directly imaging the complete velocity distribution. Using the same phase-space rotation method, we rapidly compress the cloud. Applying the cooling method a second time, we compress both the position and velocity distributions.
Tarbutt MR, 2019, Laser cooling of molecules, Contemporary Physics, Vol: 59, Pages: 356-376, ISSN: 0010-7514
Recently, laser cooling methods have been extended from atoms to molecules. The complex rotational and vibrational energy level structure of molecules makes laser cooling difficult, but these difficulties have been overcome and molecules have now been cooled to a few microkelvin and trapped for several seconds. This opens many possibilities for applications in quantum science and technology, controlled chemistry, and tests of fundamental physics. This article explains how molecules can be decelerated, cooled and trapped using laser light, reviews the progress made in recent years, and outlines some future applications.
Shyur Y, Fitch NJ, Bossert JA, et al., 2018, A high-voltage amplifier for traveling-wave Stark deceleration, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 89, ISSN: 0034-6748
Williams HJ, Caldwell L, Fitch NJ, et al., 2018, Magnetic trapping and coherent control of laser-cooled molecules, Physical Review Letters, Vol: 120, ISSN: 0031-9007
We demonstrate coherent microwave control of the rotational, hyperfine and Zeeman states of ultracold CaF molecules, and the magnetic trapping of these molecules in a single, selectable quantum state. We trap about 5 X 10³ molecules for almost 2s at a temperature of 70(8) μK and a density of 1.2 X 10⁵ cm⁻³. We measure the state-specific loss rate due to collisions with background helium.
Lim J, Almond J, Trigatzis M, et al., 2018, Laser cooled YbF molecules for measuring the electron's electric dipole moment, Physical Review Letters, Vol: 120, ISSN: 0031-9007
We demonstrate one-dimensional sub-Doppler laser cooling of a beam of YbF molecules to 100 μK. This is a key step towards a measurement of the electron's electric dipole moment using ultracold molecules. We compare the effectiveness of magnetically-assisted and polarization-gradient sub-Doppler cooling mechanisms. We model the experiment and fi nd good agreement with our data.
The ability to cool atoms below the Doppler limit -- the minimum temperaturereachable by Doppler cooling -- has been essential to most experiments withquantum degenerate gases, optical lattices and atomic fountains, among manyother applications. A broad set of new applications await ultracold molecules,and the extension of laser cooling to molecules has begun. A molecularmagneto-optical trap has been demonstrated, where molecules approached theDoppler limit. However, the sub-Doppler temperatures required for mostapplications have not yet been reached. Here we cool molecules to 50 uK, wellbelow the Doppler limit, using a three-dimensional optical molasses. Theseultracold molecules could be loaded into optical tweezers to trap arbitraryarrays for quantum simulation, launched into a molecular fountain for testingfundamental physics, and used to study ultracold collisions and ultracoldchemistry.
Williams H, Truppe S, Hambach M, et al., 2017, Characteristics of a magneto-optical trap of molecules, New Journal of Physics, Vol: 19, ISSN: 1367-2630
We present the properties of a magneto-optical trap (MOT) of CaFmolecules. We study the process of loading the MOT from a decelerated bu er-gas-cooled beam, and how best to slow this molecular beam in order to capture the most molecules. We determine how the number of molecules, the photon scattering rate, the oscillation frequency, damping constant, temperature, cloud size and lifetime depend on the key parameters of the MOT, especially the intensity and detuning of the main cooling laser. We compare our results to analytical and numerical models, to the properties of standard atomic MOTs, and to MOTs of SrF molecules. We load up to 2 x 10⁴ molecules, and measure a maximum scattering rate of 2.5 x 10⁶ s⁻¹ per molecule, a maximum oscillation frequency of 100 Hz, a maximum damping constant of 500 s⁻¹, and a minimum MOT rms radius of 1.5 mm. A minimum temperature of 730 μK is obtained by ramping down the laser intensity to low values. The lifetime, typically about 100 ms, is consistent with a leak out of the cooling cycle with a branching ratio of about 6 x 10⁻⁶. The MOT has a capture velocity of about 11 m/s.
Truppe S, Williams HJ, Fitch NJ, et al., 2017, An intense, cold, velocity-controlled molecular beam by frequency-chirped laser slowing, NEW JOURNAL OF PHYSICS, Vol: 19, ISSN: 1367-2630
Using frequency-chirped radiation pressure slowing, we precisely control the velocity of a pulsed CaF molecular beam down to a few m s–1, compressing its velocity spread by a factor of 10 while retaining high intensity: at a velocity of 15 m s–1 the flux, measured 1.3 m from the source, is 7 × 105 molecules per cm2 per shot in a single rovibrational state. The beam is suitable for loading a magneto-optical trap or, when combined with transverse laser cooling, improving the precision of spectroscopic measurements that test fundamental physics. We compare the frequency-chirped slowing method with the more commonly used frequency-broadened slowing method.
Fitch NJ, 2017, What Goes Up Must Come Down, Physics, Vol: 9
Fitch NJ, Tarbutt MR, 2016, Principles and design of a Zeeman-Sisyphus decelerator for molecular beams, ChemPhysChem, Vol: 17, Pages: 3609-3623, ISSN: 1439-4235
We explore a technique for decelerating molecules using a static magnetic field and optical pumping. Molecules travel through a spatially varying magnetic field and are repeatedly pumped into a weak-field seeking state as they move towards each strong field region, and into a strong-field seeking state as they move towards weak field. The method is time-independent and so is suitable for decelerating both pulsed and continuous molecular beams. By using guiding magnets at each weak field region, the beam can be simultaneously guided and decelerated. By tapering the magnetic field strength in the strong field regions, and exploiting the Doppler shift, the velocity distribution can be compressed during deceleration. We develop the principles of this deceleration technique, provide a realistic design, use numerical simulations to evaluate its performance for a beam of CaF, and compare this performance to other deceleration methods.
Fitch N, Tarbutt M, 2016, Principles and design of a Zeeman-Sisyphus decelerator for molecular beams, Chemphyschem, Vol: 17, Pages: 3609-3623, ISSN: 1439-7641
We explore a technique for decelerating molecules using a static magnetic eld and optical pumping. Molecules travel through a spatially varying magnetic fi eld and are repeatedly pumped into a weak-field seeking state as they move towards each strong field region, and into a strong-fi eld seeking state as they move towards weak fi eld. The method is time-independentand so is suitable for decelerating both pulsed and continuous molecular beams. By using guiding magnets at each weak field region, the beamcan be simultaneously guided and decelerated. By tapering the magnetic field strength in the strong field regions, and exploiting the Doppler shift, the velocity distribution can be compressed during deceleration. We develop the principles of this deceleration technique, provide a realistic design, use numerical simulations to evaluate its performance for a beam of CaF, and compare this performance to other deceleration methods.
Fabrikant MI, Li T, Fitch NJ, et al., 2014, Method for traveling-wave deceleration of buffer-gas beams of CH, PHYSICAL REVIEW A, Vol: 90, ISSN: 1050-2947
Parazzoli LP, Fitch NJ, Zuchowski PS, et al., 2011, Large Effects of Electric Fields on Atom-Molecule Collisions at Millikelvin Temperatures, PHYSICAL REVIEW LETTERS, Vol: 106, ISSN: 0031-9007
Fitch NJ, Weidner CA, Parazzoli LP, et al., 2009, Experimental Demonstration of Classical Hamiltonian Monodromy in the 1:1:2 Resonant Elastic Pendulum, PHYSICAL REVIEW LETTERS, Vol: 103, ISSN: 0031-9007
Parazzoli LP, Fitch N, Lobser DS, et al., 2009, High-energy-resolution molecular beams for cold collision studies, NEW JOURNAL OF PHYSICS, Vol: 11, ISSN: 1367-2630
Fitch N, Bliven W, Mitchell T, 2007, Automating data acquisition for the Cavendish balance to improve the measurement of G, AMERICAN JOURNAL OF PHYSICS, Vol: 75, Pages: 309-312, ISSN: 0002-9505
Fitch NJ, Lim J, Hinds EA, et al., Methods for measuring the electron EDM using ultracold YbF molecules
Measurements of the electron's electric dipole moment (eEDM) are demandingtests of physics beyond the Standard Model. We describe how ultracold YbFmolecules could be used to improve the precision of eEDM measurements by two tothree orders of magnitude. Using numerical simulations, we show how thecombination of magnetic focussing, two-dimensional transverse laser cooling,and frequency-chirped laser slowing, can produce an intense, slow,highly-collimated molecular beam. We show how to make a magneto-optical trap ofYbF molecules and how the molecules could be loaded into an optical lattice.eEDM measurements could be made using the slow molecular beam or usingmolecules trapped in the lattice. We estimate the statistical sensitivity thatcould be reached in each case and consider how sources of noise can be reducedso that the shot-noise limit of sensitivity can be reached. We also considersystematic effects due to magnetic fields and vector light shifts and how theycould be controlled.
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