A Rydberg quantum simulator

Abstract

Following Feynman and as elaborated on by Lloyd, a universal quantum simulator (QS) is a controlled quantum device which reproduces the dynamics of any other many particle quantum system with short range interactions. This dynamics can refer to both coherent Hamiltonian and dissipative open system evolution. Here we show that laser excited Rydberg atoms in large spacing optical or magnetic lattices provide an efficient implementation of a universal QS for spin models involving (high order) n-body interactions. This includes the simulation of Hamiltonians of exotic spin models involving n-particle constraints such as the Kitaev toric code, color code, and lattice gauge theories with spin liquid phases. In addition, it provides the ingredients for dissipative preparation of entangled states based on engineering n-particle reservoir couplings. The key basic building blocks of our architecture are efficient and high-fidelity n-qubit entangling gates via auxiliary Rydberg atoms, including a possible dissipative time step via optical pumping. This allows to mimic the time evolution of the system by a sequence of fast, parallel and high-fidelity nparticle coherent and dissipative Rydberg gates.Laser excited Rydberg atoms [1-7] stored in large spacing optical lattices [8] or magnetic trap arrays [9] offer unique possibilities for implementing scalable quantum information processors. In such a setup single atoms can be loaded and kept effectively frozen at each lattice site, with long-lived atomic ground states representing qubits or effective spin degrees of freedom. Lattice spacings of the order of a few µm allow single site addressing with laser light, and thus individual manipulation and readout of atomic spins. Exciting atoms with lasers to high-lying Rydberg states and exploiting the strong and long-range dipole-dipole or Van der Waals interactions between Rydberg states provides fast and addressable 2-qubit entangling operations or effective spin-spin interactions; recent theoretical proposals have extended Rydberg-based protocols towards a single step, high-fidelity entanglement of a mesoscopic number of atoms [10,11]. Remarkably, the basic building blocks behind such a setup have been demonstrated recently in the laboratory by several groups [12,13].Motivated by and building on these new experimental possibilities, we discuss below a Rydberg QS for many body spin models. As a key ingredient of our setup (see Fig. 1) we introduce additional auxiliary qubit atoms in the lattice, which play a two-fold role: First, they control and mediate effective n-body spin interactions among a subset of n system spins residing in their neighborhood in the lattice. In our scheme this is achieved efficiently making use of single-site addressability and a parallelized multi-qubit gate, which is based on a combination of strong and long-range Rydberg interactions and electromagnetically induced transparency (EIT), as suggested recently in Ref. [11]. Second, the auxiliary atoms can be optically pumped, thereby providing a dissipative...

Forbidden atomic transitions driven by an intensity-modulated laser trap

“…In our specific case, we have demonstrated ponderomotive spectroscopy using cold Rydberg atoms and an intensity-modulated standing-wave laser beam. One application of the method is in quantum computing 8,19 , where single-site addressability plays a central role. Another application is in precision measurement of atomic characteristics 20 and physical constants (for example, the Rydberg constant 21 , leading to the proton size 22 ); thereby, flexible spectroscopic transition rules will be very convenient.…”

Towards quantum simulating QCD

“…Highly excited Rydberg atoms in an optical lattice, which can be addressed individually with external lasers, have strong long-range dipoledipole interactions, thus allowing the entanglement of a number of atoms with a single control atom. This forms the basis of digital quantum simulator constructions for U(1) quantum link models [34,43]. These use control atoms at lattice sites to ensure Gauss' law, and at plaquette centers to flip electric flux loops, while other Rydberg atoms act as qubits that represent the quantum link variables.…”

Critical exponent of a quantum-noise-driven phase transition: The open-system Dicke model

“…The resulting dissipative Bose-Hubbard model exhibits a dynamical phase transition between a pure superfluid state and a thermal-like mixed state as the onsite interaction is increased [10]. Note that this method for the preparation of strongly correlated quantum states makes dissipation to be a resource for quantum simulation [11] and universal quantum computation [12].…”