May 22 2017
Fascinating enough, apparently independent pendulum clocks can function together and tick in synchrony at the same time. Occurring often in nature as well as engineering, the “self-organized synchronization” phenomenon is one of the important research areas of Marc Timme and his colleagues from the Max Planck Institute for Dynamics and Self-Organization.
Several pendulum clocks can synchronize to one frequency of oscillation as if by magic when they have a common suspension. Christiaan Huygens observed this phenomenon for the first time in 1665. CREDIT: Henrique M. Oliveira and Luís V. Melo.
The physicists from Göttingen form a part of a German-Italian partnership that has recently reported an astonishing finding in the journal Nature Communications—quantum systems also have the ability to be synchronized by means of self-organization, without the need for an external control. The synchronization can be readily perceived by means of a quite unusual characteristic of the quantum realm, namely, entanglement.
In the year 1665, Christiaan Huygens (1629–1695), a Dutch researcher, was striving to develop an innovative clock for ships. During that period, pendulum clocks were considered to be the most modern, and a uniquely shaped pendulum was proposed to respond less sensitively to the rocking of the ships. The accurate working of the clocks in the ship was highly important for the precise calculation of the longitude. For safety purposes, Huygens had designed two of his pendulum clocks to be enclosed inside a heavy housing, suspended such that it predominantly compensates for the rocking of the ship. Then, he found out an astonishing phenomenon—while the clocks worked independent of one another and were not affected by any external disturbances, the pendulums of the clock swung in accurate synchrony within not more than half an hour after each restart.
Even at that time, Huygens deduced that the two pendulums synchronized through tiny “imperceptible motions” occurring in the joint suspension of the two clocks. His theory proved to be correct because physicists could later demonstrate such oscillating systems. “One can observe such clocks as well as many other oscillating objects to synchronize with each other even in the absence of any external influence,” explained Marc Timme, a theoretical physicist at the Max Planck Institute for Dynamics and Self-Organization in Göttingen, who heads a Research Group that investigates the dynamics of networks and analyses, such as the behavior of electricity grids.
A joint suspension causes the pendulums to synchronize
The self-organized synchronization of apparently independent pendulums to one frequency can be detected in many systems in nature and engineering. More often, the precondition is a “hidden” coupling, similar to the joint suspension for the pendulum clocks. Researchers such as Timme also term this a locking behavior, wherein all oscillators get involved in synchronizing accurately to one frequency and then stay confined in it. Such a behavior originally also works well with children’s swings hung from a joint beam. When they are swung from disparate starting positions, they can get synchronized to a single frequency at some point.
The examples are not just restricted to mechanical oscillations. “Synchronization also happens for many different biological networks,” explained Timme “The phenomenon for instance occurs in the brain when nerve impulses synchronize.” Such a synchronization of brain waves in specific areas appears to be significant for the operation of the brain. However, it can also function too high. “Large-scale, extensive synchronization of brain waves in the brain is characteristic for epilepsy,” stated Timme.
Quantum objects synchronize without any external influence
Such self-organized ordering phenomena are dependent on the basic principles of the classical–non-quantum world. Yet, a German-Italian research partnership has now unearthed synchronization arising even in the case of pure quantum systems. The partnership was initiated by Marc Timme along with his erstwhile postdoc Dirk Witthaut, who meanwhile leads an independent research team at the Forschungszentrum Jülich. The conceptually innovative study has at present been reported in the renowned journal Nature Communications. In the study, for the first time, the researchers have exhibited that isolated systems containing large numbers of quantum objects (e.g. atoms of a Bose-Einstein condensate confined in an optical lattice) have the ability to synchronize in a manner very similar to classical physics systems.
The Nobel Prize in Physics for the year 2001 was awarded for experimentally realizing a Bose-Einstein condensate, wherein the behavior of a number of atoms in the condensate is similar to that of a single quantum object. However, individual atoms can be confined in an optical lattice. Grids such as these are built from the electromagnetic potential of crossed laser beams and are similar to an egg box formed of light, where the atoms are scattered. The quantum particles can get synchronized inside the box without the need for any external impact, implying that they are similarly self-organized. “This is the main news of our article,” stated Timme.
Such oscillating quantum systems can be taken similar to a number of Huygens’ pendulum clocks. The clocks are connected with one another by means of a beam through which they are suspended. As a result, the pendulums of the clocks oscillate synchronously after a specific time period. The quantum systems get similarly synchronized by interacting with one another. Such a self-organized transition to a synchronized collective completely correlates with classical physics.
Synchronized quantum objects are entangled
However, there is something more that occurs in the quantum realm—a collective quantum state is formed. Such a quantum state portrayed the unpredictability of quantum mechanics as such—entanglement. Quantum systems intertwined with one another can no longer be delineated independent of one another. In this example of the clocks, it would be something like the pendulums can no longer be individually recognized, that is, each pendulum will include information related to all other pendulums. Hence all the pendulums would act together like one object, that is, a quantum object. “Classical synchronization is the ‘smoking gun’ for the formation of quantum mechanical entanglement,” stated Dirk Witthaut, lead author of the study, “and this is extremely surprising.”
The discovery illuminates an astonishing phenomenon of entanglement. For many decades, entangled systems have been consistently created in many physics laboratories. The outcomes of this study are not only significant for basic research. For quite some time, the focus of the quantum information research area has been to use entanglement as a technical resource, either in futuristic quantum computers or in the error-proof transfer of information. The article published by the German-Italian partnership at present also offers tangible schemes related to the manner in which self-organized synchronization of a quantum collective can be analyzed in the lab. Hence it will be interesting to observe the form in which the phenomenon actually occurs and the manner in which it inspires new areas of research.
For Marc Timme, this paper also proves as a proof of the significance of the partnership between different disciplines in discovering such extraordinary phenomena. Specifically, Timme is himself an expert on the dynamics of classical self-organizing systems and synchronization. His research fields are termed “nonlinear dynamics” and “network dynamics.” “Nonlinear dynamics” is also widely termed as “chaos theory.” On the contrary, Dirk Witthaut belongs to the area of quantum physics. It is the intense partnership between the two fields in physics that resulted in the finding that classical synchronization in the quantum realm is connected to quantum mechanical entanglement. “It is often very difficult to fund and carry out such interdisciplinary projects in particular, because they cannot be assigned to any of the traditional disciplines,” stated Timme. The successful outcome in Göttingen was feasible as the Max Planck Society supported the interdisciplinary study in the long term and as pure research without a predetermined aim.