The quantum statistics of atoms is typically observed in the behavior of an ensemble via macroscopic observables. However, quantum statistics modifies the behavior of even two particles. Here, we demonstrate near-complete control over all the internal and external degrees of freedom of two laser-cooled (87)Rb atoms trapped in two optical tweezers. This controllability allows us to observe signatures of indistinguishability via two-particle interference. Our work establishes laser-cooled atoms in optical tweezers as a promising route to bottom-up engineering of scalable, low-entropy quantum systems.

We demonstrate rapid loading of a small array of optical tweezers with a single 87 Rb atom per site. We find that loading efficiencies of up to 90% per tweezer are achievable in less than 170 ms for traps separated by more than 1.7 µm. Interestingly, we find the load efficiency is affected by nearby traps and present the efficiency as a function of the spacing between two optical tweezers. This enhanced loading, combined with subsequent rearranging of filled sites, will enable the study of quantum many-body systems via quantum gas assembly.A frontier in atomic physics is the study of quantum many-body physics on a microscopic scale. Recent experiments have shown the power of microscopy of degenerate quantum gases in optical lattices [1,2]. An exciting prospect is not only imaging quantum gases, but assembling them into a well-known initial configuration from single-atom building blocks and then observing the resulting dynamics with single-atom resolution. Wavelength-scale optical dipole traps, or optical tweezers, are an attractive platform for control of neutral atoms because they allow repositioning of the atoms after state preparation and site-resolved imaging. Using optical tweezers, long-range interactions between neutral atoms have been harnessed via Rydberg blockade [3-5], and it is now possible to observe controlled interactions and interference between bosonic and fermionic atoms placed individually in their motional ground state [6][7][8]. While optical tweezer traps can be scaled to arrays [9][10][11][12], realizing an ordered array with a single atom per trap is difficult and is a problem of long-standing interest [13][14][15][16].Early experiments with optical tweezers demonstrated sub-Poissonian atom-number statistics using light-assisted collisions that rapidly expel pairs of atoms, a process known as collisional blockade [17][18][19][20]. This has become a reliable method to isolate single atoms, as well as the basis for parity imaging in quantum-gas microscopes [1,2,17]. However, the collisional blockade also limits loading efficiencies to approximately 50%, making the probability to uniformly-fill large arrays prohibitively small [18][19][20].Careful studies of light-assisted collisions in optical dipole traps hold promise for realizing deterministic loading of arrays of atoms [16,21]. Light-assisted collisions are successfully described by transitions between molecular potentials that become resonant with the light at specific interatomic separations, R C [ Fig. 1(a)] [22]. In the case of light that is red-detuned from the bare atomic transition, the atoms associate to an attractive potential and can gain a large kinetic energy, leading to loss of both atoms from the trap. Conversely, when the light is blue-detuned, the atoms associate to a repulsive potential where the maximum kinetic energy gained is set by the detuning [23]. This control has been used to preferentially expel single 85 Rb atoms from a trap, enabling the isolation of single atoms with high probability [16,21]. However, open q...

We study the response of graphene to high-intensity 10^11-10^12 Wcm^-2, 50-femtosecond laser pulse excitation. We establish that graphene has a fairly high (~3\times10^12Wcm^-2) single-shot damage threshold. Above this threshold, a single laser pulse cleanly ablates graphene, leaving microscopically defined edges. Below this threshold, we observe laser-induced defect formation that leads to degradation of the lattice over multiple exposures. We identify the lattice modification processes through in-situ Raman microscopy. The effective lifetime of CVD graphene under femtosecond near-IR irradiation and its dependence on laser intensity is determined. These results also define the limits of non-linear applications of graphene in femtosecond high-intensity regime.Comment: 4 pages, 3 figure