A quantum gas microscope - detecting single atoms in a Hubbard regime optical lattice
📝 Abstract
Recent years have seen tremendous progress in creating complex atomic many-body quantum systems. One approach is to use macroscopic, effectively thermodynamic ensembles of ultracold atoms to create quantum gases and strongly correlated states of matter, and to analyze the bulk properties of the ensemble. The opposite approach is to build up microscopic quantum systems atom by atom - with complete control over all degrees of freedom. Until now, the macroscopic and microscopic strategies have been fairly disconnected. Here, we present a “quantum gas microscope” that bridges the two approaches, realizing a system where atoms of a macroscopic ensemble are detected individually and a complete set of degrees of freedom of each of them is determined through preparation and measurement. By implementing a high-resolution optical imaging system, single atoms are detected with near-unity fidelity on individual sites of a Hubbard regime optical lattice. The lattice itself is generated by projecting a holographic mask through the imaging system. It has an arbitrary geometry, chosen to support both strong tunnel coupling between lattice sites and strong on-site confinement. On one hand, this new approach can be used to directly detect strongly correlated states of matter. On the other hand, the quantum gas microscope opens the door for the addressing and read-out of large-scale quantum information systems with ultracold atoms.
💡 Analysis
Recent years have seen tremendous progress in creating complex atomic many-body quantum systems. One approach is to use macroscopic, effectively thermodynamic ensembles of ultracold atoms to create quantum gases and strongly correlated states of matter, and to analyze the bulk properties of the ensemble. The opposite approach is to build up microscopic quantum systems atom by atom - with complete control over all degrees of freedom. Until now, the macroscopic and microscopic strategies have been fairly disconnected. Here, we present a “quantum gas microscope” that bridges the two approaches, realizing a system where atoms of a macroscopic ensemble are detected individually and a complete set of degrees of freedom of each of them is determined through preparation and measurement. By implementing a high-resolution optical imaging system, single atoms are detected with near-unity fidelity on individual sites of a Hubbard regime optical lattice. The lattice itself is generated by projecting a holographic mask through the imaging system. It has an arbitrary geometry, chosen to support both strong tunnel coupling between lattice sites and strong on-site confinement. On one hand, this new approach can be used to directly detect strongly correlated states of matter. On the other hand, the quantum gas microscope opens the door for the addressing and read-out of large-scale quantum information systems with ultracold atoms.
📄 Content
A quantum gas microscope – detecting single atoms in a Hubbard regime optical lattice Waseem S. Bakr, Jonathon I. Gillen, Amy Peng, Simon Fölling, Markus Greiner Harvard-MIT Center for Ultracold Atoms and Dept. Of Physics, Harvard University, Cambridge, Massachusetts 02138, USA Recent years have seen tremendous progress in creating complex atomic many-body quantum systems. One approach is to use macroscopic, effectively thermodynamic ensembles of ultracold atoms to create quantum gases and strongly correlated states of matter, and to analyze the bulk properties of the ensemble. For example, bosonic and fermionic atoms in a Hubbard regime optical lattice 1, 2, 3, 4, 5 allow experimenters to carry out quantum simulations of solid state models 6, thereby addressing fundamental questions of condensed matter physics. The opposite approach is to build up microscopic quantum systems atom by atom – with complete control over all degrees of freedom 7, 8, 9. The atoms or ions act as qubits and allow experimenters to realize quantum gates with the goal of creating highly controllable quantum information systems. Until now, the macroscopic and microscopic strategies have been fairly disconnected. Here, we present a “quantum gas microscope” that bridges the two approaches, realizing a system where atoms of a macroscopic ensemble are detected individually and a complete set of degrees of freedom of each of them is determined through preparation and measurement. By implementing a high-resolution optical imaging system, single atoms are detected with near-unity fidelity on individual sites of a Hubbard regime optical lattice. The lattice itself is generated by projecting a holographic mask through the imaging system. It has an arbitrary geometry, chosen to support both strong tunnel coupling between lattice sites and strong on-site confinement. On one hand, this new approach can be used to directly detect strongly correlated states of matter. In the context of condensed matter simulation, this corresponds to the detection of individual electrons in the simulated crystal with atomic resolution. On the other hand, the quantum gas microscope opens the door for the addressing and read- out of large-scale quantum information systems with ultracold atoms. In Hubbard-regime optical lattice systems an atomic quantum gas resides in a multi- dimensional array of lattice sites 10. Strongly correlated quantum states such as bosonic and fermionic Mott insulator states have been created in such lattices 2, 4, 5, and the realization of quantum magnetism and d-wave superfluidity is being actively pursued 11, 12, 6. Experiments of this type have for the most part relied on measuring ensemble properties such as global coherence and compressibility. Creating the possibility of probing the quantum gas with single atom – single lattice site resolution, in contrast, would allow experimenters to access the quantum gas on a single “qubit” level and measure the particle-particle correlation functions that characterize strongly correlated quantum states. The quantum gas microscope provides exactly this capability through an unprecedented combination of resolution and sensitivity. It is based on a number of innovations such as a solid immersion microscopy for cold atoms, a two-dimensional optical lattice in close vicinity to an optical surface, and the use of incoherent lattice light. The microscope enables the detection of single atoms with near unity fidelity on single lattice sites of a short period optical lattice in the Hubbard model regime. Previously, site-resolved optical imaging of single atoms has been demonstrated in lattices with large spacings (5 micrometer period) and in sparsely populated 1D arrays 13, 14. Imaging of 2D arrays of “tubes” with large occupations has been shown for smaller spacings with an electron microscope 15 and optical imaging 16 systems. For the described applications, however, a combination of high fidelity single atom detection and short lattice periods are important, which has not been previously achieved. Small lattice spacings on the order of 500 nm are required to ensure usable scales of tunnel coupling and interaction strength in the Hubbard model regime, and to generate a macroscopic ensemble with all atoms in the on- site ground state (lowest Bloch band). We demonstrate high fidelity site-resolved single atom detection in such a lattice, by which all spatial degrees of freedom of each atom are then fully determined. The quantum gas microscope is based on a high aperture optical system, which simultaneously serves to generate the lattice potential and detect single atoms with site-resolved resolution. By placing a 2D quantum gas only a few microns away from the front surface of this microscope, we are able to achieve a very high numerical aperture of NA=0.8. As a result, we measure an optical resolution of ~ 600 nm (full width, half maximum , FWHM). Unlike typ
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