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arXiv:2505.08413 · Physical Review A

Improved delta-kick cooling with multiple nonideal kicks

Harshil Neeraj, David Spierings, Joseph McGowan, Nicholas Mantella, Aephraim M. Steinberg

Published Jun 9, 2026• 0 citations

Abstract

Delta-kick cooling is a technique employed to achieve low kinetic temperatures by decreasing momentum width at the cost of increased position width. In an ideal implementation, this method uses a harmonic potential to deliver a single near-instantaneous momentum kick. In practice, potentials that are approximately harmonic near their center are commonly used. As a result, the breakdown of the harmonic approximation far from the center limits the cooling performance. Inspired by aberration cancellation in optics, we propose to use compound matter-wave lens systems for $δ-$kick cooling with Gaussian potentials. By strategically combining attractive and repulsive kicks, we show that it is possible to mimic the effect of a harmonic potential. For a test case with reasonable experimental parameters, our method suggests a reduction in kinetic temperature by a factor of $2.5$ using a 2-pulse sequence and by a factor of $3.2$ using a 3-pulse sequence.

DOI: 10.1103/sr5h-xhct

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Delta-kick cooling is a technique employed to achieve low kinetic temperatures by decreasing momentum width at the cost of increased position width. In an ideal implementation, this method uses a harmonic potential to deliver a single near-instantaneous momentum kick. In practice, potentials that are approximately harmonic near their center are commonly used. As a result, the breakdown of the harmonic approximation far from the center limits the cooling performance. Inspired by aberration cancellation in optics, we propose to use compound matter-wave lens systems for

δ-

kick cooling with Gaussian potentials. By strategically combining attractive and repulsive kicks, we show that it is possible to mimic the effect of a harmonic potential. For a test case with reasonable experimental parameters, our method suggests a reduction in kinetic temperature by a factor of

2.5

using a 2-pulse sequence and by a factor of

3.2

using a 3-pulse sequence.

We present an improved and simplified version of ``\ensuremath{\delta}-kick cooling.'' By application of a pulsed magnetic field, laser-cooled Rb atoms are cooled in one dimension, by a factor of 10 below the temperature of optical molasses. While phase-space density is conserved in this process, the method is more efficient than adiabatic expansion. We have achieved temperatures below 700 nK, but there is no fundamental limit to this cooling technique. The technique can also be used as an atom lens and as a spin-dependent probe. We show preliminary results suggesting interesting spin-temperature correlations within an optical molasses.

Delta-kick cooling (DKC) is used to compress the momentum distribution of ultracold quantum matter. It combines expansion dynamics with the use of kick pulses, designed via classical methods, that bring the system to rest. We introduce an exact approach to DKC for arbitrary scale-invariant dynamics of quantum gases, lifting the original restrictions to free evolution and noninteracting systems, to account for the control of atomic clouds in a time-dependent harmonic trap that can be either repulsive (inverted) or confining. We show that DKC assisted by a repulsive potential outperforms the conventional scheme, and that sudden trap-frequency quenches combined with DKC are equivalent to time-optimal bang-bang protocols. We further show that reverse engineering of the scale-invariant dynamics under smooth trap-frequency modulations can be combined with DKC to introduce a new class of shortcuts to adiabaticity assisted by kicks.

We present a new technique for cooling atoms below the photon recoil temperature. Free expansion and a subsequent application of a pulsed potential narrows the momentum distribution provided the atoms were initially well localized. Time scales for this cooling mechanism are shorter than those for other techniques. We give the one dimensional results for quantum and classical distributions of atoms initially held in an optical lattice or a dipole trap. The pulsed lattice potential is the same as that used in the recent atom optics realization of the quantum delta kicked rotor.

We implement and demonstrate the effectiveness of a cooling scheme using a moving, all-optical, one-way barrier to cool a sample of

^{87}\mathrm{Rb}

atoms, achieving nearly a factor of 2 reduction in temperature. The one-way barrier, composed of two focused, Gaussian laser beams, allows atoms incident on one side to transmit, while reflecting atoms incident on the other. The one-way barrier is adiabatically swept through a sample of atoms contained in a far-off-resonant, single-beam, optical dipole trap that forms a nearly harmonic trapping potential. As the barrier moves longitudinally through the potential, atoms become trapped to one side of the barrier with reduced kinetic energy. The adiabatic translation of the barrier leaves the atoms at the bottom of the trapping potential, only minimally increasing their kinetic energy.

We present progress towards a planned experiment on atomic tunneling of ultra-cold Rb atoms. As a first step in this experiment we present a realization of an improved form of "delta-kick cooling." By application of a pulsed magnetic field, laser cooled Rb atoms are further cooled by a factor of 10 (in 1-D) over the temperature out of molasses. Temperatures below 700 nK are observed. The technique can be used not only to cool without fundamental limit (but conserving phase-space density), but also to focus atoms, and as a spin-dependent probe.