Observation of Collisions between Two Ultracold Ground-State CaF Molecules

Cheuk, Lawrence; Anderegg, Loïc; Bao, Yicheng; Burchesky, Sean; Yu, Scarlett S.; Ketterle, Wolfgang; Ni, Kang-Kuen; Doyle, John M.

doi:10.1103/physrevlett.125.043401

Cited by 112 publications

(102 citation statements)

References 58 publications

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“…This is consistent with previous observations [25], and the absence of collisional energy shifts or decoherence may be expected as short-range collisions in the gas lead to loss of molecules with high probability [35][36][37][38]. Measurements of the coherence out to longer times will require confinement of the molecules to a 3D optical lattice [39] , optical tweezers [40][41][42], or the use of alternative trapping techniques such as a blue-detuned optical trap [43] to avoid losses from the optical excitation of two-molecule collision complexes [36,44]. The creation of controlled arrays of molecules is also a key component of the proposed quantum computing protocols where storage qubits have applications; our method of using a magic-polarisation trap is compatible with the confinement of molecules to arrays of optical tweezers or a 3D optical lattice [45].…”

supporting

confidence: 90%

Robust storage qubits in ultracold polar molecules

Gregory

Blackmore

Bromley³

et al. 2021

Preprint

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Quantum states with long-lived coherence are essential for quantum computation, simulation and metrology. The nuclear spin states of ultracold molecules prepared in the singlet rovibrational ground state are an excellent candidate for encoding and storing quantum information. However, it is important to understand all sources of decoherence for these qubits, and then eliminate them, in order to reach the longest possible coherence times. Here, we fully characterise the dominant mechanisms for decoherence of a storage qubit in an optically trapped ultracold gas of RbCs molecules using high-resolution Ramsey spectroscopy. Guided by a detailed understanding of the hyperfine structure of the molecule, we tune the magnetic field to where a pair of hyperfine states have the same magnetic moment. These states form a qubit, which is insensitive to variations in magnetic field. Our experiments reveal an unexpected differential tensor light shift between the states, caused by weak mixing of rotational states. We demonstrate how this light shift can be eliminated by setting the angle between the linearly polarised trap light and the applied magnetic field to a magic angle of arccos(1/√3)≈55°. This leads to a coherence time exceeding 6.9 s (90% confidence level). Our results unlock the potential of ultracold molecules as a platform for quantum computation.

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supporting

confidence: 90%

Robust storage qubits in ultracold polar molecules

Gregory

Blackmore

Bromley³

et al. 2021

Preprint

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“…In a temperature regime down to a few tens of nanokelvin, highly controllable polar molecules provide scientists with a powerful apparatus to study a vast range of new quantum phenomena in condensed matter physics, quantum information processing, and quantum chemistry (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14), such as exotic quantum phases (15)(16)(17)(18), quantum gates with fast switching times (19,20), and quantum chemical reactions (9)(10)(11)(12)(13). In all these studies, the two-body loss is an essential ingredient leading to non-Hermitian phenomena.…”

Section: Introductionmentioning

confidence: 99%

Universal relations for ultracold reactive molecules

Lin

et al. 2020

Sci. Adv.

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The realization of ultracold polar molecules in laboratories has pushed physics and chemistry to new realms. In particular, these polar molecules offer scientists unprecedented opportunities to explore chemical reactions in the ultracold regime where quantum effects become profound. However, a key question about how two-body losses depend on quantum correlations in interacting many-body systems remains open so far. Here, we present a number of universal relations that directly connect two-body losses to other physical observables, including the momentum distribution and density correlation functions. These relations, which are valid for arbitrary microscopic parameters, such as the particle number, the temperature, and the interaction strength, unfold the critical role of contacts, a fundamental quantity of dilute quantum systems, in determining the reaction rate of quantum reactive molecules in a many-body environment. Our work opens the door to an unexplored area intertwining quantum chemistry; atomic, molecular, and optical physics; and condensed matter physics.

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“…By transferring laser-cooled 40 Ca 19 F molecules from a magneto-optical trap (MOT) into an optical dipole trap and finally into an array of optical tweezers, it has been possible to manipulate the quantum states and control the collisions of individual pairs of molecules. This enabled the study of collisions between pairs of CaF molecules with unprecedented precision 58,156 . Two optical tweezer traps, each featuring a single state-selected CaF molecule (including selection of hyperfine states), were merged.…”

Section: Reactions In the Ultracold Regime Below 1 Mkmentioning

confidence: 99%

Towards chemistry at absolute zero

Heazlewood¹,

Softley

2021

Nat Rev Chem

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The prospect of cooling matter down to temperatures that are close to the absolute zero raises intriguing questions about how chemical reactivity changes under these extreme conditions. Although some types of chemical reaction still occur at 1 µK, they can no longer adhere to the conventional picture of reactants passing over an activation energy barrier to become products. Indeed at ultracold temperatures, the system enters a fully quantum regime, and quantum mechanics replaces the classical picture of colliding particles. In this Review, we discuss recent experimental and theoretical developments that allow us to explore chemical reactions at temperatures that range from 10 K to 500 nK. Although the field is still in its infancy, exceptional control has already been demonstrated over reactivity at low temperatures.ultracold temperatures, the classical description of the collision of particles needs to be replaced with a quantum description and the picture of a ball rolling over a hill needs to be replaced by that of a wave propagating across a barrier.The quantum regime is a physical regime in which our basic understanding of how chemical processes happen, in terms of molecules bumping into each other and breaking and remaking bonds, needs to be challenged. Strictly speaking, the dynamical system of moving and colliding molecules needs to be described as a superposition of partial waves, the components of which represent the different angular momentum states associated with the relative motion of the colliding particles. As the temperature is lowered, the system moves towards a regime in which it can be described by just a few quantised collisional angular momentum states (and, ultimately, just a single state). We denote the collisions as 's-wave' or 'p-wave' collisions (known as the partial-wave description) to represent those with zero or one unit of collisional angular momentum, respectively. Furthermore, in the quantum regime the population of molecular quantum states is distributed over just a few rovibrational states and ultimately collapses to a single quantum state at the lowest temperatures (under conditions of thermal equilibrium). At low temperatures, quantum effects on the rate coefficient and other properties of the reaction, such as collision energy resonances, quantum reflection and geometric phase (described in detail in the 'Reactions in the ultracold regime' section), are most likely to be observable. This is in contrast to what we observe at room temperature, where we understand the overall rate of a process to be an average of the behaviours of individual collisions of molecules with vastly varying sets of quantum numbers and a distribution of energies.When the temperature reaches sub-µK, the translational wavelength typically exceeds the average separation of molecules in the sample, even for a low density gas, and ultimately the system may enter the regime of quantum degeneracy (for example, bosonic particles that form a Bose-Einstein condensate, in which all particles are in the same quan...

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Observation of Collisions between Two Ultracold Ground-State CaF Molecules

Cited by 112 publications

References 58 publications

Robust storage qubits in ultracold polar molecules

Robust storage qubits in ultracold polar molecules

Universal relations for ultracold reactive molecules

Towards chemistry at absolute zero

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