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Multipartite entangled microwave and micromechanical squeezed Schr\"{o}dinger cats: a phase transition-based protocol

Adil A. Gangat, Ian P. McCulloch, Gerard J Milburn

Published Nov 19, 2012• 0 citations
OpenAlex

Abstract

Electromechanical systems currently offer a path to engineering quantum states of microwave and micromechanical modes that are of both fundamental and applied interest. Particularly desirable, but not yet observed, are mechanical states that exhibit entanglement, wherein non-classical correlations exist between distinct modes; squeezing, wherein the quantum uncertainty of an observable quantity is reduced below the standard quantum limit; and Schrodinger cats, wherein a single mode is cast in a quantum superposition of macroscopically distinct classical states. Also, while most investigations of electromechanical systems have focussed on single- or few-body scenarios, the many-body regime remains virtually unexplored. In such a regime quantum phase transitions naturally present themselves as a resource for quantum state generation, thereby providing a route toward entangling a large number of electromechanical systems in highly non-classical states. Here we show how to use existing superconducting circuit technology to implement a (quasi) quantum phase transition in an array of electromechanical systems such that entanglement, squeezing, and Schrodinger cats become simultaneously observable across multiple microwave and micromechanical oscillators.

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Electromechanical systems currently offer a path to engineering quantum states of microwave and micromechanical modes that are of both fundamental and applied interest. Particularly desirable, but not yet observed, are mechanical states that exhibit entanglement, wherein non-classical correlations exist between distinct modes; squeezing, wherein the quantum uncertainty of an observable quantity is reduced below the standard quantum limit; and Schrodinger cats, wherein a single mode is cast in a quantum superposition of macroscopically distinct classical states. Also, while most investigations of electromechanical systems have focussed on single- or few-body scenarios, the many-body regime remains virtually unexplored. In such a regime quantum phase transitions naturally present themselves as a resource for quantum state generation, thereby providing a route toward entangling a large number of electromechanical systems in highly non-classical states. Here we show how to use existing superconducting circuit technology to implement a (quasi) quantum phase transition in an array of electromechanical systems such that entanglement, squeezing, and Schrodinger cats become simultaneously observable across multiple microwave and micromechanical oscillators.
Electromechanical systems currently offer a path to engineering quantum states of microwave and micromechanical modes that are of both fundamental and applied interest. Particularly desirable, but not yet observed, are mechanical states that exhibit entanglement, wherein non-classical correlations exist between distinct modes; squeezing, wherein the quantum uncertainty of an observable quantity is reduced below the standard quantum limit; and Schrödinger cats, wherein a single mode is cast in a quantum superposition of macroscopically distinct classical states. Also, while most investigations of electromechanical systems have focussed on single- or few-body scenarios, the many-body regime remains virtually unexplored. In such a regime quantum phase transitions naturally present themselves as a resource for quantum state generation, thereby providing a route toward entangling a large number of electromechanical systems in highly non-classical states. Here we show how to use existing superconducting circuit technology to implement a (quasi) quantum phase transition in an array of electromechanical systems such that entanglement, squeezing, and Schrödinger cats become simultaneously observable across multiple microwave and micromechanical oscillators.
Schrödinger's cat originates from the famous thought experiment querying the counterintuitive quantum superposition of macroscopic objects. As a natural extension, several "cats" (quasi-classical objects) can be prepared into coherent quantum superposition states, which is known as multipartite cat states demonstrating quantum entanglement among macroscopically distinct objects. Here, we present a highly scalable approach to deterministically create flying multipartite Schrödinger's cat states by reflecting coherent-state photons from a microwave cavity containing a superconducting qubit. We perform full quantum state tomography on the cat states with up to four photonic modes and confirm the existence of quantum entanglement among them. We also witness the hybrid entanglement between discrete-variable states (the qubit) and continuous-variable states (the flying multipartite cat) through a joint quantum state tomography. Our work provides an enabling step for implementing a series of quantum metrology and quantum information processing protocols based on cat states.
Quantum-electromechanical systems are nanoscale mechanical resonators whose high-frequency oscillations are detected by an electronic transducer. Despite their macroscopic size and mechanical, ordinary-matter nature, these resonators can exhibit distinct quantum behavior that is of great interest and promise to an experimental exploration of questions in the foundations of quantum mechanics. After a brief introduction to quantum-electromechanical systems, I will sketch the feasibility and features of superposition states of macroscopically distinct positions in such systems. I will also show how these systems give rise to a new and hitherto hardly explored decoherence model and present some first results for this model.
Over the last decade and a half, superconducting circuits have advanced to the point where we can generate and detect highly-entangled states, and perform universal quantum gates. Meanwhile, the coherence properties of these systems have improved more than 10,000-fold. I will describe recent experiments, such as the latest advance in coherence using a three-dimensional implementation of qubits interacting with microwave cavities, called “3D circuit QED.” The control and strong interactions possible in superconducting circuits make it possible to generate non-classical states of light, including large superpositions known as “Schrodinger cat” states. This field has many interesting prospects both for applications in quantum information processing, and fundamental investigations of the boundary between the macroscopic classical world and the microscopic world of the quantum.
Schrödinger cat states, consisting of superpositions of macroscopically distinct states, provide key resources for a large number of emerging quantum technologies in quantum information processing. Here we propose how to generate and manipulate mechanical and optical Schrödinger cat states with distinguishable superposition components by exploiting the unique properties of cavity optomechanical systems based on Bose-Einstein condensate. Specifically, we show that in comparison with its solid-state counterparts, almost a 3 order of magnitude enhancement in the size of the mechanical Schrödinger cat state could be achieved, characterizing a much smaller overlap between its two superposed coherent-state components. By exploiting this generated cat state, we further show how to engineer the quadrature squeezing of the mechanical mode. Besides, we also provide an efficient method to create multicomponent optical Schrödinger cat states in our proposed scheme. Our work opens up a new way to achieve nonclassical states of massive objects, facilitating the development of fault-tolerant quantum processors and sensors.
Two-mode squeezing is a fascinating example of quantum entanglement manifested in cross-correlations of non-commuting observables between two subsystems. At the same time, these subsystems themselves may contain no quantum signatures in their self-correlations. These properties make two-mode squeezed (TMS) states an ideal resource for applications in quantum communication. Here, we generate propagating microwave TMS states by a beam splitter distributing single mode squeezing emitted from distinct Josephson parametric amplifiers along two output paths. We experimentally study the fundamental dephasing process of quantum cross-correlations in continuous-variable propagating TMS microwave states and accurately describe it with a theory model. In this way, we gain the insight into finite-time entanglement limits and predict high fidelities for benchmark quantum communication protocols such as remote state preparation and quantum teleportation.