We study an experimentally feasible qubit system employing neutral atomic currents. Our system is based on bosonic cold atoms trapped in ring-shaped optical lattice potentials. The lattice makes the system strictly one dimensional and it provides the infrastructure to realize a tunable ring-ring interaction. Our implementation combines the low decoherence rates of neutral cold atoms systems, overcoming single site addressing, with the robustness of topologically protected solid state Josephson flux qubits. Characteristic fluctuations in the magnetic fields affecting Josephson junction based flux qubits are expected to be minimized employing neutral atoms as flux carriers. By breaking the Galilean invariance we demonstrate how atomic currents through the lattice provide an implementation of a qubit. This is realized either by artificially creating a phase slip in a single ring, or by tunnel coupling of two homogeneous ring lattices. The single qubit infrastructure is experimentally investigated with tailored optical potentials. Indeed, we have experimentally realized scaled ring-lattice potentials that could host, in principle, n ~ 10 of such ring-qubits, arranged in a stack configuration, along the laser beam propagation axis. An experimentally viable scheme of the two-ring-qubit is discussed, as well. Based on our analysis, we provide protocols to initialize, address, and read-out the qubit.

We consider a correlated Bose gas tightly confined into a ring shaped lattice, in the presence of an artificial gauge potential inducing a persistent current through it. A weak link painted on the ring acts as a source of coherent back-scattering for the propagating gas, interfering with the forward scattered current. This system defines an atomic counterpart of the rf-SQUID: the atomtronics quantum interference device. The goal of the present study is to corroborate the emergence of an effective twolevel system in such a setup and to assess its quality, in terms of its inner resolution and its separation from the rest of the many-body spectrum, across the different physical regimes. In order to achieve this aim, we examine the dependence of the qubit energy gap on the bosonic density, the interaction strength, and the barrier depth, and we show how the superposition between current states appears in the momentum distribution (time-of-flight) images. A mesoscopic ring lattice with intermediate-tostrong interactions and weak barrier depth is found to be a favorable candidate for setting up, manipulating and probing a qubit in the next generation of atomic experiments. through a small spatial region, where an effective potential constriction (giving rise to the aforementioned weak link) is created via a very focused blue-detuned laser or via a painting potential [20][21][22][23].On the theoretical side, it has been demonstrated that the two currents flowing in the AQUID can, indeed, define an effective two-level system, that is, the cold-atom analog of flux qubits [24,25]. The potential constriction breaks the Galilean invariance and splits the qubit levels that otherwise would be perfectly degenerate at half-flux quantum. In this context, it is of vital importance for the qubit dynamics that a good energy resolution of the two levels could be achieved in realistic physical situations (while keeping the qubit well separated from the rest of the many-body spectrum).In this paper we focus on ring-shaped confinements with a lattice modulation and a potential constriction. This set-up, that can be realized following different routes (see, e.g., [25]), presents several advantages for the design of an AQUID. First of all, assuming that the bosons occupy only the lowest Bloch band 8 , the ring lattice helps in controlling the current. For instance, because of the one-dimensional dynamics, the vortex formation rate along the flow is negligible. Secondly, it helps localizing the barrier effect to a point-like scale with respect to lattice spacing, which should in turn yield a favorable scaling of the qubit gap with the bosonic density [27]. Moreover, it provides an easy route to realize interacting ring-ring architectures [14,25] This issue has been considered so far only in some limiting cases, e.g. for particular types of superposition states or in the infinitely strong interacting regime [27,29]. We perform a systematic study on the quality of the qubit in the cold-atom ring lattice: in particular, we characterize the en...

Atomtronics deals with matter-wave circuits of ultracold atoms manipulated through magnetic or laser-generated guides with different shapes and intensities. In this way, new types of quantum networks can be constructed in which coherent fluids are controlled with the know-how developed in the atomic and molecular physics community. In particular, quantum devices with enhanced precision, control, and flexibility of their operating conditions can be accessed. Concomitantly, new quantum simulators and emulators harnessing on the coherent current flows can also be developed. Here, the authors survey the landscape of atomtronics-enabled quantum technology and draw a roadmap for the field in the near future. The authors review some of the latest progress achieved in matter-wave circuits' design and atom-chips. Atomtronic networks are deployed as promising platforms for probing many-body physics with a new angle and a new twist. The latter can be done at the level of both equilibrium and nonequilibrium situations. Numerous relevant problems in mesoscopic physics, such as persistent currents and quantum transport in circuits of fermionic or bosonic atoms, are studied through a new lens. The authors summarize some of the atomtronics quantum devices and sensors. Finally, the authors discuss alkali-earth and Rydberg atoms as potential platforms for the realization of atomtronic circuits with special features.