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arXiv:1211.4302

Non-locally entangled microwave and micromechanical squeezed cats: a phase transition-based protocol

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

Published Nov 19, 2012• 0 citations
arXivHTMLPDF

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 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.

DOI
10.48550/arxiv.1211.4302

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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 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.
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.
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.
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.
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.
Abstract Mechanical systems facilitate the development of a hybrid quantum technology comprising electrical, optical, atomic and acoustic degrees of freedom1, and entanglement is essential to realize quantum-enabled devices. Continuous-variable entangled fields—known as Einstein–Podolsky–Rosen (EPR) states—are spatially separated two-mode squeezed states that can be used for quantum teleportation and quantum communication2. In the optical domain, EPR states are typically generated using nondegenerate optical amplifiers3, and at microwave frequencies Josephson circuits can serve as a nonlinear medium4–6. An outstanding goal is to deterministically generate and distribute entangled states with a mechanical oscillator, which requires a carefully arranged balance between excitation, cooling and dissipation in an ultralow noise environment. Here we observe stationary emission of path-entangled microwave radiation from a parametrically driven 30-micrometre-long silicon nanostring oscillator, squeezing the joint field operators of two thermal modes by 3.40 decibels below the vacuum level. The motion of this micromechanical system correlates up to 50 photons per second per hertz, giving rise to a quantum discord that is robust with respect to microwave noise7. Such generalized quantum correlations of separable states are important for quantum-enhanced detection8 and provide direct evidence of the non-classical nature of the mechanical oscillator without directly measuring its state9. This noninvasive measurement scheme allows to infer information about otherwise inaccessible objects, with potential implications for sensing, open-system dynamics and fundamental tests of quantum gravity. In the future, similar on-chip devices could be used to entangle subsystems on very different energy scales, such as microwave and optical photons.