Recent ideas and technological developments have made possible studies of macroscopic objects deep in the quantum regime. In the talk I will discuss the experiment where an entangled Einstein-Podolsky-Rosen (EPR) state has been generated between distant mechanical and atomic oscillators [1]. The concept of an oscillator with an effective negative mass crucial for those experiments will be presented. Such entanglement allows to measure disturbances in the position and the momentum of an oscillator simultaneously, the trait which may seem counterintuitive. Using this entangled state, the trajectory of motion of the oscillator in phase space can be traced with, in principle, unlimited accuracy. Progress towards application of those ideas to gravitational wave detectors [2] following the proposals [3], [4] will be reported.
Recent ideas and technological developments have made possible studies of macroscopic objects deep in the quantum regime. In the talk I will discuss the experiment where an entangled Einstein-Podolsky-Rosen (EPR) state has been generated between distant mechanical and atomic oscillators [1]. The concept of an oscillator with an effective negative mass crucial for those experiments will be presented. Such entanglement allows to measure disturbances in the position and the momentum of an oscillator simultaneously, the trait which may seem counterintuitive. Using this entangled state, the trajectory of motion of the oscillator in phase space can be traced with, in principle, unlimited accuracy. Progress towards application of those ideas to gravitational wave detectors [2] following the proposals [3], [4] will be reported.
Significant achievements in high-sensitivity measurements will soon allow us to probe quantum behaviors of macroscopic mechanical oscillators. In a recent work [Phys. Rev. A 80, 043802 (2009)], we formulated a general framework for treating preparation of Gaussian quantum states of macroscopic oscillators through linear position measurements. To outline a complete procedure for testing macroscopic quantum mechanics, here we consider a subsequent verification stage which probes the prepared macroscopic quantum state and verifies the quantum dynamics. By adopting an optimal time-dependent homodyne detection in which the phase of the local oscillator varies in time, the conditional quantum state can be characterized below the Heisenberg limit, thereby achieving a quantum tomography. In the limiting case of no readout loss, such a scheme evades measurement-induced back action, which is identical to the variational-type measurement scheme invented by Vyatchanin et al. [JETP 77, 218 (1993)] but in the context for detecting gravitational waves. To motivate macroscopic quantum mechanics experiments with future gravitational-wave detectors, we mostly focus on the parameter regime where the characteristic measurement frequency is much higher than the oscillator frequency and the classical noises are Markovian, which captures the main feature of a broadband gravitational-wave detector. In addition, we discuss verifications of Einstein-Podolsky-Rosen-type entanglement between macroscopic test masses in future gravitational-wave detectors, which enables us to test one particular version of gravity decoherence conjectured by Di\'osi [Phys. Lett. A120, 377 (1987)] and Penrose [Gen. Rel. Grav. 28, 581 (1996)].
This Colloquium examines the field of the EPR Gedankenexperiment, from the original paper of Einstein, Podolsky and Rosen, through to modern theoretical proposals of how to realize both the continuous-variable and discrete versions of the EPR paradox. We analyze the relationship with entanglement and Bell's theorem, and summarize the progress to date towards experimental confirmation of the EPR paradox, with a detailed treatment of the continuous-variable paradox in laser-based experiments. Practical techniques covered include continuous-wave parametric amplifier and optical fibre quantum soliton experiments. We discuss current proposals for extending EPR experiments to massive-particle systems, including spin-squeezing, atomic position entangle- ment, and quadrature entanglement in ultra-cold atoms. Finally, we examine applications of this technology to quantum key distribution, quantum teleportation and entanglement-swapping.
The Physics of Quantum Information is getting mature enough, in the laboratory and in ground based applications, to consider the possibility of future Space extensions. The nonlocal properties of Einstein-Podolsky-Rosen entangled states might define a new frontier both in the field of remote communications and in the astronomical detectors of the new generation. Here we present: (1) a communication technique based on the use of entangled pairs in polarization states, organized in bunches with precise statistically correlated distributions. (2) In addition we briefly discuss the conceptual development of gravitational wave (GW) detectors based on Quantum Entangled STate (QUEST) technology.
Quantum correlations are essential for achieving quantum advantage in computing, communication and sensing. Moreover, their observation challenges and constrains our fundamental understanding of nature. Mechanical oscillators in the quantum regime provide an appealing platform for preparing and investigating quantum correlations at macroscopic scales. Despite substantial progress, however, continuous-variable quantum correlations stronger than entanglement have not yet been observed in this macroscopic regime. Here, we report the experimental observation of continuous-variable Einstein-Podolsky-Rosen correlations between two spatially-separated mechanical oscillators with an effective mass of ∼16μg each. This is achieved by coupling them to a superconducting qubit which allows for engineering a two-mode squeezing interaction when parametrically driven. Crucially, we show that this interaction can be used to witness quantum correlations through the realization of a mechanical SU(1,1) interferometer. Our results expand the toolbox of operations in circuit quantum acoustodynamics and demonstrate that quantum correlations stronger than entanglement can also be observed in macroscopic systems, thereby shedding light on the boundary between quantum and classical regimes.
This Colloquium examines the field of the Einstein, Podolsky, and Rosen (EPR) gedanken experiment, from the original paper of Einstein, Podolsky, and Rosen, through to modern theoretical proposals of how to realize both the continuous-variable and discrete versions of the EPR paradox. The relationship with entanglement and Bell's theorem are analyzed, and the progress to date towards experimental confirmation of the EPR paradox is summarized, with a detailed treatment of the continuous-variable paradox in laser-based experiments. Practical techniques covered include continuous-wave parametric amplifier and optical fiber quantum soliton experiments. Current proposals for extending EPR experiments to massive-particle systems are discussed, including spin squeezing, atomic position entanglement, and quadrature entanglement in ultracold atoms. Finally, applications of this technology to quantum key distribution, quantum teleportation, and entanglement swapping are examined.
Eugene Polzik's recent article on the ability of physicists to "entangle" large numbers of atoms for long periods of time (Physics World September pp33–37) illustrates how new technology has revolutionized quantum measurement and information. It is now possible, for example, to demonstrate experimentally key paradoxes of quantum mechanics. These include the famous Einstein–Podolsky–Rosen (EPR) paradox that if the position and momenta of two distant particles are correlated, then knowing the position or momentum of one particle immediately reveals the position and momentum of the other–without any physical measurement having to be made.