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Register a new userFloquet Hamiltonian Engineering of an Isolated Many-Body Spin System
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Controlling interactions is the key element for quantum engineering of many-body systems. Using time-periodic driving, a naturally given many-body Hamiltonian of a closed quantum system can be transformed into an effective target Hamiltonian exhibiting vastly different dynamics. We demonstrate such Floquet engineering with a system of spins represented by Rydberg states in an ultracold atomic gas. Applying a sequence of spin manipulations, we change the symmetry properties of the effective Heisenberg XYZ Hamiltonian. As a consequence, the relaxation behavior of the total spin is drastically modified. The observed dynamics can be qualitatively captured by a semi-classical simulation. Synthesising a wide range of Hamiltonians opens vast opportunities for implementing quantum simulation of non-equilibrium dynamics in a single experimental setting.
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We experimentally demonstrate how thermal properties in an non-equilibrium quantum many- body system emerge locally, spread in space and time, and finally lead to the globally relaxed state. In our experiment, we quench a one-dimensional (1D) Bose gas by coherently splitting it into two parts. By monitoring the phase coherence between the two parts we observe that the thermal correlations of a prethermalized state emerge locally in their final form and propagate through the system in a light-cone-like evolution. Our results underline the close link between the propagation of correlations and relaxation processes in quantum many-body systems.
We experimentally investigate the action of a localized dissipative potential on a macroscopic matter wave, which we implement by shining an electron beam on an atomic Bose-Einstein condensate (BEC). We measure the losses induced by the dissipative potential as a function of the dissipation strength observing a paradoxical behavior when the strength of the dissipation exceeds a critical limit: for an increase of the dissipation rate the number of atoms lost from the BEC becomes lower. We repeat the experiment for different parameters of the electron beam and we compare our results with a simple theoretical model, finding excellent agreement. By monitoring the dynamics induced by the dissipative defect we identify the mechanisms which are responsible for the observed paradoxical behavior. We finally demonstrate the link between our dissipative dynamics and the measurement of the density distribution of the BEC allowing for a generalized definition of the Zeno effect. Due to the high degree of control on every parameter, our system is a promising candidate for the engineering of fully governable open quantum systems.
Ultracold atoms are an ideal platform to study strongly correlated phases of matter in and out of equilibrium. Much of the experimental progress in this field crucially relies on the control of the contact interaction between two atoms. Control of strong long-range interactions between distant ground state atoms has remained a long standing goal, opening the path towards the study of fundamentally new quantum many-body systems including frustrated or topological magnets and supersolids. Optical dressing of ground state atoms by near-resonant laser coupling to Rydberg states has been proposed as a versatile method to engineer such interactions. However, up to now the great potential of this approach for interaction control in a many-body setting has eluded experimental confirmation. Here we report the realisation of coherent Rydberg-dressing in an ultracold atomic lattice gas and directly probe the induced interaction potential using an interferometric technique with single atom sensitivity. We use this approach to implement a two-dimensional synthetic spin lattice and demonstrate its versatility by tuning the range and anisotropy of the effective spin interactions. Our measurements are in remarkable agreement with exact solutions of the many-body dynamics, providing further evidence for the high degree of accurate interaction control in these systems. Finally, we identify a collective many-body decay process, and discuss possible routes to overcome this current limitation of coherence times. Our work marks the first step towards the use of laser-controlled Rydberg interactions for the study of exotic quantum magnets in optical lattices.
Coherent control via periodic modulation, also known as Floquet engineering, has emerged as a powerful experimental method for the realization of novel quantum systems with exotic properties. In particular, it has been employed to study topological phenomena in a variety of different platforms. In driven systems, the topological properties of the quasienergy bands can often be determined by standard topological invariants, such as Chern numbers, which are commonly used in static systems. However, due to the periodic nature of the quasienergy spectrum, this topological description is incomplete and new invariants are required to fully capture the topological properties of these driven settings. Most prominently, there exist two-dimensional anomalous Floquet systems that exhibit robust chiral edge modes, despite all Chern numbers are equal to zero. Here, we realize such a system with bosonic atoms in a periodically-driven honeycomb lattice and infer the complete set of topological invariants from energy gap measurements and local Hall deflections.
We introduce a new approach for the robust control of quantum dynamics of strongly interacting many-body systems. Our approach involves the design of periodic global control pulse sequences to engineer desired target Hamiltonians that are robust against disorder, unwanted interactions and pulse imperfections. It utilizes a matrix representation of the Hamiltonian engineering protocol based on time-domain transformations of the Pauli spin operator along the quantization axis. This representation allows us to derive a concise set of algebraic conditions on the sequence matrix to engineer robust target Hamiltonians, enabling the simple yet systematic design of pulse sequences. We show that this approach provides an efficient framework to (i) treat any secular many-body Hamiltonian and engineer it into a desired form, (ii) target dominant disorder and interaction characteristics of a given system, (iii) achieve robustness against imperfections, (iv) provide optimal sequence length within given constraints, and (v) substantially accelerate numerical searches of pulse sequences. Using this systematic approach, we develop novel sets of pulse sequences for the protection of quantum coherence, optimal quantum sensing and quantum simulation. Finally, we experimentally demonstrate the robust operation of these sequences in a system with the most general interaction form.
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