Blue-Detuned Magneto-Optical Trap

Jarvis, K. N.; Devlin, J. A.; Wall, T. E.; Sauer, B. E.; Tarbutt, M. R.

doi:10.1103/physrevlett.120.083201

Cited by 34 publications

(30 citation statements)

References 39 publications

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“…To this end, we have presented the equations in a general form so that they can be used by others. We have already used our model to study a blue-detuned MOT of 87 Rb [33], and to investigate laser cooling of SrF and YbF molecules [4], where we find the same qualitative behavior as described here for CaF. Future applications include the study of MOTs for molecules with very different energy level structures, the investigation of Λ-enhanced gray molasses cooling [34] and other novel cooling schemes, and the study of laser cooling within optical dipole traps [35].…”

Section: Discussionmentioning

confidence: 99%

Laser cooling and magneto-optical trapping of molecules analyzed using optical Bloch equations and the Fokker-Planck-Kramers equation

Devlin

Tarbutt

2018

Phys. Rev. A

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We study theoretically the behavior of laser-cooled calcium monofluoride (CaF) molecules in an optical molasses and magneto-optical trap (MOT), and compare our results to recent experiments. We use multi-level optical Bloch equations to estimate the force and the diffusion constant, followed by a Fokker-Planck-Kramers equation to calculate the time-evolution of the velocity distribution. The calculations are done in three-dimensions, and we include all the relevant energy levels of the molecule and all the relevant frequency components of the light. Similar to simpler model systems, the velocity-dependent force curve exhibits Doppler and polarization-gradient forces of opposite signs. We show that the temperature of the MOT is governed mainly by the balance of these two forces. Our calculated MOT temperatures and photon scattering rates are in broad agreement with those measured experimentally over a wide range of parameters. In a blue-detuned molasses, the temperature is determined by the balance of polarization gradient cooling, and heating due to momentum diffusion, with no significant contribution from Doppler heating. In the molasses, we calculate a damping rate similar to the measured one, and steady-state temperatures that have the same dependence on laser intensity and applied magnetic field as measured experimentally, but are consistently a few times smaller than measured. We attribute the higher temperatures in the experiments to fluctuations of the dipole force which are not captured by our model. We show that the photon scattering rate is strongly influenced by the presence of dark states in the system, but that the scattering rate does not go to zero even for stationary molecules because of the transient nature of the dark states.

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Section: Discussionmentioning

confidence: 99%

Laser cooling and magneto-optical trapping of molecules analyzed using optical Bloch equations and the Fokker-Planck-Kramers equation

Devlin

Tarbutt

2018

Phys. Rev. A

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“…At a lower intensity, I t = 30 mW/cm 2 , the temperature varies between 32 and 38 µK as ∆ 21 /(2π) is varied between 35 and 47 MHz. The first blue-detuned MOT configuration was characterized in some detail in [12]. Here, we extend that study by measuring the capture velocity and the rate coefficient for trap loss due to The capture velocity, v c , is an important parameter of a MOT that governs the steady-state trapped atom number and atom density through the loading rate of the trap [13,14].…”

Section: Blue-detuned Motsmentioning

confidence: 81%

“…We have observed two configurations of blue-detuned MOT. In the first configuration, presented in [12], L 1 is detuned from F = 1, and L 2 is detuned from F = 2. In the second combination, both lasers are detuned from F = 1.…”

Section: Blue-detuned Motsmentioning

confidence: 99%

“…Recently, a number of groups have demonstrated magneto-optical trapping of diatomic molecules [6][7][8], which are cooled using type-II transitions [9], and this has generated a renewed interest in understanding the properties of type-II MOTs [10,11]. This new understanding led us to propose and demonstrate a novel MOT, where blue-detuned light drives type-II transitions [12]. This MOT performed exceptionally well, providing a phase-space density far higher than reported in any other type-II MOT, and comparable with the very best type-I MOTs.…”

Section: Introductionmentioning

confidence: 99%

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Characteristics of unconventional Rb magneto-optical traps

2018

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We study several new magneto-optical trapping configurations in 87 Rb. These unconventional MOTs all use type-II transitions, where the angular momentum of the ground state is greater than or equal to that of the excited state, and they may use either red-detuned or blue-detuned light. We describe the conditions under which each new MOT forms. The various MOTs exhibit an enormous range of lifetimes, temperatures and density distributions. At the detunings where they are maximized, the lifetimes of the various MOTs vary from 0.1 to 15 s. One MOT forms large ring-like structures with no density at the centre. The temperature in the red-detuned MOTs can be three orders of magnitude higher than in the blue-detuned MOTs. We present measurements of the capture velocity of a blue-detuned MOT, and we study how the loss rate due to ultracold collisions depends on laser intensity and detuning. arXiv:1807.07655v1 [physics.atom-ph]

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“…Cooling of an atomic gas to the required temperatures requires a multi-stage process: laser cooling in a magneto-optical trap (MOT); sub-Doppler cooling; loading into a conservative magnetic or optical trap; evaporative cooling. Although quite efficient, this process is only possible for a small subset of alkali and alkali-earth-like atoms that can be initially cooled to low temperature by optical means.The sub-Doppler cooling phase typically uses light red detuned from the F → F = F + 1 cycling transition of a D 2 line nS 1/2 → nP 3/2 [4], and can be understood in terms of the "Sisyphus effect" [5][6][7][8]. Sub-Doppler cooling schemes involving dark states (DSs) [9] have emerged as a powerful alternative; they are known as gray molasses.…”

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confidence: 99%

Loading and cooling in an optical trap via hyperfine dark states

Naik

Eneriz-imaz

Carey

et al. 2020

Phys. Rev. Research

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We present a novel optical cooling scheme that relies on hyperfine dark states to enhance loading and cooling atoms inside deep optical dipole traps. We demonstrate a seven-fold increase in the number of atoms loaded in the conservative potential with strongly shifted excited states. In addition, we use the energy selective dark-state to efficiently cool the atoms trapped inside the conservative potential rapidly and without losses. Our findings open the door to optically assisted cooling of trapped atoms and molecules which lack the closed cycling transitions normally needed to achieve low temperatures and the high initial densities required for evaporative cooling.Ultra-cold quantum gases have attracted much attention in recent decades as versatile platforms for investigating strongly correlated quantum systems [1] and as the basis for a new class of quantum technologies based on atomic interferometry [2,3]. Cooling of an atomic gas to the required temperatures requires a multi-stage process: laser cooling in a magneto-optical trap (MOT); sub-Doppler cooling; loading into a conservative magnetic or optical trap; evaporative cooling. Although quite efficient, this process is only possible for a small subset of alkali and alkali-earth-like atoms that can be initially cooled to low temperature by optical means.The sub-Doppler cooling phase typically uses light red detuned from the F → F = F + 1 cycling transition of a D 2 line nS 1/2 → nP 3/2 [4], and can be understood in terms of the "Sisyphus effect" [5][6][7][8]. Sub-Doppler cooling schemes involving dark states (DSs) [9] have emerged as a powerful alternative; they are known as gray molasses. Very recently they have been pivotal in obtaining an alloptical BEC in microgravity [10] and a degenerate Fermi gas of polar molecules [11]. The DSs are coherent superpositions of internal and external (momentum) states that are decoupled from the optical field; their creation does not require cycling F → F = F + 1 transitions, but can rely on any transitions of the F → F ≤ F form.To prevent the expansion of the cold atom cloud during cooling, it is tempting to combine DS sub-Doppler cooling with spatial confinement in a far-off-resonance optical dipole trap (FORT). However, the DSs are then strongly modified by the trap potential, which typically shortens their lifetime and eventually couples them to the light field.In this letter, we show that DS cooling can be used in combination with FORT when strong differential light * devang.naik@institutoptique.fr † andrea.bertoldi@institutoptique.fr shift are present. We use the effect of FORT trapping light close the 5P 3/2 → 4D 3/2;5/2 transitions of rubidium at 1529 nm [12,13] to maximize the cooling action on the surrounding of the trap and at its borders. We observe an order of magnitude improvement in the number of trapped atoms. Additionally, we explore the possibility of cooling the atomic ensemble in the FORT. We achieve a notable temperature reduction of the trapped sample in a few ms and without losing atoms and analyz...

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Blue-Detuned Magneto-Optical Trap

Cited by 34 publications

References 39 publications

Laser cooling and magneto-optical trapping of molecules analyzed using optical Bloch equations and the Fokker-Planck-Kramers equation

Laser cooling and magneto-optical trapping of molecules analyzed using optical Bloch equations and the Fokker-Planck-Kramers equation

Characteristics of unconventional Rb magneto-optical traps

Loading and cooling in an optical trap via hyperfine dark states

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