We propose a scheme to create coherent superpositions of annular flow of strongly-interacting bosonic atoms in a 1D ring trap. The non-rotating ground state is coupled to a vortex state with mesoscopic angular momentum by means of a narrow potential barrier and an applied phase that originates from either rotation or a synthetic magnetic field. We show that superposition states in the Tonks-Girardeau regime are robust against single-particle loss due to the effects of strong correlations. The coupling between the mesoscopically distinct states scales much more favorably with particle number than in schemes relying on weak interactions, thus making particle numbers of hundreds or thousands feasible. Coherent oscillations induced by time variation of parameters may serve as a 'smoking gun' signature for detecting superposition states.
We present a theoretical and numerical analysis of a quantum system that is capable of functioning as a heat engine. This system could be realized experimentally using cold bosonic atoms confined to a double well potential that is created by splitting a harmonic trap with a focused laser. The system shows thermalization, and can model a reversible heat engine cycle. This is the first demonstration of the operation of a heat engine with a finite quantum heat bath.
The advent of increasingly precise gyroscopes has played a key role in the technological development of navigation systems. Ring-laser and fiber-optic gyroscopes, for example, are widely used in modern inertial guidance systems and rely on the interference of unentangled photons to measure mechanical rotation. The sensitivity of these devices scales with the number of particles used as 1/ √ N . Here we demonstrate how, by using sources of entangled particles, it is possible to do better and even achieve the ultimate limit allowed by quantum mechanics where the precision scales as 1/N. We propose a gyroscope scheme that uses ultracold atoms trapped in an optical ring potential.
We present a scheme for creating macroscopic superpositions of the direction of superfluid flow around a loop. Using the Bose-Hubbard model we study an array of Bose-Einstein condensates trapped in optical potentials and coupled to one another to form a ring. By rotating the ring so that each particle acquires on average half a quantum of superfluid flow, it is possible to create a multiparticle superposition of all the particles rotating and all the particles stationary. Under certain conditions it is possible to scale up the number of particles to form a macroscopic superposition. The simplicity of the model has allowed us to study macroscopic superpositions at an atomic level for different variables. Here we concentrate on the tunnelling strength between the potentials. Further investigation remains important, because it could lead us to making an ultra-precise quantum-limited gyroscope.Superpositions are one of the defining differences between classical and quantum mechanics. To test whether quantum mechanics can describe the macroscopic world, which would normally be described classically, we will look for superpositions in larger systems. Multiparticle superposition states have been observed in a number of systems including photons [1], C 60 molecules [2], and the internal state of four 9 Be + ions [3]. Experimental signatures of larger scale quantum phenomenon were shown when Rouse et al.[4] observed resonant tunnelling between two macroscopically distinct states in a superconducting quantum interference device (SQUID). The observed tunnelling was between states of different flux or opposite currents flowing around a loop. Macroscopic systems consist of approximately 10 10 particles or have a macroscopic measurable quantity associated with them. The currents measured in the SQUID consisted of approximately 10 9 Cooper pairs and produce a measurable magnetic flux, meaning tunnelling between two macroscopically distinct states had been achieved. Similar systems have also been used to show cat states can be made [5,6].Bose-Einstein condensates (BECs) are a promising system for realising similar results. They are composed of 10 3 −10 7 atoms with a high proportion in the same quantum state and are sufficiently cold to undergo a quantum phase transition from superfluid to Mott insulator [7]. They also have significant advantages over SQUIDs since they are highly controllable: the coupling between condensates and the strength of the interactions between atoms can be tuned over many orders of magnitude, there are few imperfections and near perfect lattices can be created. This enables us to develop a simple model to investigate macroscopic quantum effects [8]. SQUIDS have the advantage that a precise magnetic field can be applied to the system, which produces an easily controllable phase around the loop. This maybe more difficult for BECs.There have already been a number of theoretical pro-posals for producing cat states with BECs in a range of different set-ups [9]. In this paper, we present a scheme for produci...
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