28 results found
Barontini G, Blackburn L, Boyer V, et al., 2021, Measuring the stability of fundamental constants with a network of clocks, Publisher: arXiv
The detection of variations of fundamental constants of the Standard Modelwould provide us with compelling evidence of new physics, and could lift theveil on the nature of dark matter and dark energy. In this work, we discuss howa network of atomic and molecular clocks can be used to look for suchvariations with unprecedented sensitivity over a wide range of time scales.This is precisely the goal of the recently launched QSNET project: A network ofclocks for measuring the stability of fundamental constants. QSNET will includestate-of-the-art atomic clocks, but will also develop next-generation molecularand highly charged ion clocks with enhanced sensitivity to variations offundamental constants. We describe the technological and scientific aims ofQSNET and evaluate its expected performance. We show that in the range ofparameters probed by QSNET, either we will discover new physics, or we willimpose new constraints on violations of fundamental symmetries and a range oftheories beyond the Standard Model, including dark matter and dark energymodels.
Barontini G, Boyer V, Calmet X, et al., 2021, QSNET, a network of clock for measuring the stability of fundamental constants, Proceedings Volume 11881, Quantum Technology: Driving Commercialisation of an Enabling Science II, Publisher: SPIE, Pages: 1-4
The QSNET consortium is building a UK network of next-generation atomic and molecular clocks that will achieve unprecedented sensitivity in testing variations of the fine structure constant, α, and the electron-to-proton mass ratio, μ. This in turn will provide more stringent constraints on a wide range of fundamental and phenomenological theories beyond the Standard Model and on dark matter models.
Greenberg J, Krohn OA, Bossert JA, et al., 2021, Velocity-tunable beam of continuously decelerated polar molecules for cold ion-molecule reaction studies., Rev Sci Instrum, Vol: 92
Producing high densities of molecules is a fundamental challenge for low-temperature, ion-molecule reaction studies. Traveling-wave Stark decelerators promise to deliver high density beams of cold, polar molecules but require non-trivial control of high-voltage potentials. We have overcome this experimental challenge and demonstrate continuous deceleration of ND3 from 385 to 10 m/s, while driving the decelerator electrodes with a 10 kV amplitude sinewave. In addition, we test an alternative slowing scheme, which increases the time delay between decelerated packets of ND3 and non-decelerated molecules, allowing for better energy resolution of subsequent reaction studies. We characterize this source of neutral, polar molecules suitable for energy-resolved reaction studies with trapped ions at cold translational temperatures. We also propose a combined apparatus consisting of the traveling-wave decelerator and a linear ion trap with a time-of-flight mass spectrometer and discuss to what extent it may achieve cold, energy-resolved, ion-neutral reactions.
Alauze X, Lim J, Trigatzis MA, et al., 2021, An ultracold molecular beam for testing fundamental physics, QUANTUM SCIENCE AND TECHNOLOGY, Vol: 6, ISSN: 2058-9565
Fitch N, Tarbutt M, 2021, Laser-cooled molecules, Advances in Atomic Molecular and Optical Physics, ISSN: 1049-250X
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, Quantum Sci. Technol., Vol: 6
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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