Imperial College London

DrHannahWilliams

Faculty of Natural SciencesDepartment of Physics

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hannah.williams10

 
 
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Blackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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10 results found

Scholl P, Schuler M, Williams HJ, Eberharter AA, Barredo D, Schymik K-N, Lienhard V, Henry L-P, Lang TC, Lahaye T, Läuchli AM, Browaeys Aet al., 2021, Quantum simulation of 2D antiferromagnets with hundreds of Rydberg atoms., Nature, Vol: 595, Pages: 233-238

Quantum simulation using synthetic systems is a promising route to solve outstanding quantum many-body problems in regimes where other approaches, including numerical ones, fail1. Many platforms are being developed towards this goal, in particular based on trapped ions2-4, superconducting circuits5-7, neutral atoms8-11 or molecules12,13. All of these platforms face two key challenges: scaling up the ensemble size while retaining high-quality control over the parameters, and validating the outputs for these large systems. Here we use programmable arrays of individual atoms trapped in optical tweezers, with interactions controlled by laser excitation to Rydberg states11, to implement an iconic many-body problem-the antiferromagnetic two-dimensional transverse-field Ising model. We push this platform to a regime with up to 196 atoms manipulated with high fidelity and probe the antiferromagnetic order by dynamically tuning the parameters of the Hamiltonian. We illustrate the versatility of our platform by exploring various system sizes on two qualitatively different geometries-square and triangular arrays. We obtain good agreement with numerical calculations up to a computationally feasible size (approximately 100 particles). This work demonstrates that our platform can be readily used to address open questions in many-body physics.

Journal article

Jurgilas S, Chakraborty A, Rich CJH, Caldwell L, Williams HJ, Fitch NJ, Sauer BE, Frye MD, Hutson JM, Tarbutt MRet al., 2021, Collisions between Ultracold Molecules and Atoms in a Magnetic Trap, PHYSICAL REVIEW LETTERS, Vol: 126, ISSN: 0031-9007

Journal article

Schymik KN, Lienhard V, Barredo D, Scholl P, Williams H, Browaeys A, Lahaye Tet al., 2020, Enhanced atom-by-atom assembly of arbitrary tweezer arrays, Physical Review A, Vol: 102, ISSN: 2469-9926

We report on improvements extending the capabilities of the atom-by-atom assembler described by Barredo et al. [Science 354, 1021 (2016)SCIEAS0036-807510.1126/science.aah3778] that we use to create fully-loaded target arrays of more than 100 single atoms in optical tweezers, starting from randomly loaded, half-filled initial arrays. We describe four variants of the sorting algorithm that decrease the number of moves needed for assembly and enable the assembly of arbitrary, nonregular target arrays. We demonstrate experimentally the performance of this enhanced assembler for a variety of target arrays.

Journal article

Caldwell L, Williams H, Fitch N, Aldegunde J, Hutson J, Sauer B, Tarbutt Met 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.

Journal article

Caldwell L, Devlin J, Williams H, Fitch N, Hinds E, Sauer B, Tarbutt Met 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.

Journal article

Williams HJ, Caldwell L, Fitch NJ, Truppe S, Rodewald J, Hinds EA, Sauer BE, Tarbutt MRet 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.

Journal article

Truppe S, Williams HJ, Hambach M, Caldwell L, Fitch NJ, Hinds EA, Sauer BE, Tarbutt MRet al., 2017, Molecules cooled below the Doppler limit, Nature Physics, Vol: 13, Pages: 1173-1176, ISSN: 1745-2473

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.

Journal article

Williams H, Truppe S, Hambach M, Caldwell L, Fitch N, Hinds E, Sauer B, Tarbutt Met 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.

Journal article

Truppe S, Williams HJ, Fitch NJ, Hambach M, Wall TE, Hinds EA, Sauer BE, Tarbutt MRet 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.

Journal article

Miralles V, Huerre A, Williams H, Fournie B, Jullien M-Cet al., 2015, A versatile technology for droplet-based microfluidics: thermomechanical actuation, LAB ON A CHIP, Vol: 15, Pages: 2133-2139, ISSN: 1473-0197

Journal article

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