Single-spin addressing in an atomic Mott insulator

Abstract

Ultracold atoms in optical lattices are a versatile tool to investigate fundamental properties of quantum many body systems. In particular, the high degree of control of experimental parameters has allowed the study of many interesting phenomena such as quantum phase transitions and quantum spin dynamics. Here we demonstrate how such control can be extended down to the most fundamental level of a single spin at a specific site of an optical lattice. Using a tightly focussed laser beam together with a microwave field, we were able to flip the spin of individual atoms in a Mott insulator with sub-diffraction-limited resolution, well below the lattice spacing. The Mott insulator provided us with a large two-dimensional array of perfectly arranged atoms, in which we created arbitrary spin patterns by sequentially addressing selected lattice sites after freezing out the atom distribution. We directly monitored the tunnelling quantum dynamics of single atoms in the lattice prepared along a single line and observed that our addressing scheme leaves the atoms in the motional ground state. Our results open the path to a wide range of novel applications from quantum dynamics of spin impurities, entropy transport, implementation of novel cooling schemes, and engineering of quantum many-body phases to quantum information processing.The ability to observe and control the position of single atoms on a surface of a solid via scanning tunnelling and atomic force microscopy has revolutionised the field of condensed matter physics [1,2]. In few-atom systems, coherent control of single particles in e.g. an ion chain has proven crucial for the implementation of high-fidelity quantum gates and the readout of individual qubits in quantum information processing [3]. Bringing such levels of control to the regime of large scale many-body systems has been a longstanding goal in quantum physics. In the context of ultracold atoms in optical lattices, a major challenge has been to combine degenerate atomic samples with single-site addressing resolution and singleatom sensitivity. This full control is essential for many applications in condensed matter physics, such as the study of spin impurities [4] and quantum spin dynamics [5,6] within quantum magnetism, entropy transport, the implementation of novel cooling schemes [7,8] or digital quantum simulations based on Rydberg atoms [9]. For scalable quantum information processing, a Mott insulator with unity filling provides a natural quantum register with several hundreds of qubits. In order to exploit the full potential of such a large scale system for quantum computation, coherent manipulation of individual spins is indispensable, both within a circuit-based [10] or a one-way quantum computer architecture [11,12].The quest to address atoms on single sites of an optical lattice has a long history [7,[13][14][15][16][17][18][19][20][21][22]. In one dimension, single-site addressing was accomplished optically † present address: Department of Physics and Astronomy, University of Aarhus, DK-8000 ...

Exploring the quantum speed limit with computer games

“…Several proposals for the implementation of quantum computing in this system have been proposed, mainly using long range gates or contact interactions [11]. Here we investigate an architecture [6] where contact interaction is achieved by moving atoms on top of each other using a so-called optical tweezer [22,23], a tightly focused off-resonant laser beam. Finding the optimal motion of the tweezer from one lattice site to another is a difficult problem when the available time is close to the QSL, and it is this transfer problem that is introduced to the players of Quantum Moves through different challenges.…”

Fermionic transport and out-of-equilibrium dynamics in a homogeneous Hubbard model with ultracold atoms

“…the averaged group velocity of the Bloch waves (see SI G). This expansion can be seen as a continuous quantum walk [20][21][22][23][24]. For comparison, classical (thermal) hopping of a particle (e.g.…”

Comparing and contrasting nuclei and cold atomic gases

“…However, recently microtraps have been built that are capable of trapping very few atoms (1 − 10) at very low temperatures (Serwane et al 2011, Zürn et al 2012. Furthermore, it is now possible to address single lattice sites in an optical lattice and produce and probe only a few atoms on such a site (Bakr et al 2010, Sherson et al 2010, Weitenberg et al 2011). These developments provide hope that aspects of nuclear physics can be simulated with cold atomic gas setups in a very direct manner.…”

“…The goal is to discuss universal features of these quantum states and phases and investigate whether they can be manifest in fewbody systems with nuclei as the example. A particularly interesting venture at a time when trapping of small samples of only a few atoms have been realized experimentally (Serwane et al 2011, Zürn et al 2012, Bakr et al 2010, Sherson et al 2010, Weitenberg et al 2011, implying that systems resembling few-body nuclei can be produced and studied in cold atomic gase experiments.…”

“…Typically, these system contain thousands or even millions of particles, but very recently samples with very small particle numbers have been realized (Serwane et al 2011, Zürn et al 2012, Bakr et al 2010, Sherson et al 2010, Weitenberg et al 2011). This regime is particularly interesting since the physics that can be learned here might aid our understanding of mesoscopic and microscopic systems in other subfields.…”