Scientists Realize Optical Version of Schrödinger’s Thought Experiment

Flying Optical Cats for Quantum Communication

Dead and alive: Schrödinger’s cat is entangled with an atom. If the atom is excited, the cat is alive. If it has decayed, the cat is dead. In the experiment, a light pulse represents the two states (peaks) and may be in a superposition of both, just like the cat. © Christoph Hohmann, Nanosystems Initiative Munich (NIM)

An old thought experiment now appears in a new light. In 1935 Erwin Schrödinger formulated a thought experiment designed to capture the paradoxical nature of quantum physics. A group of researchers led by Gerhard Rempe, Director of the Department of Quantum Dynamics at the Max Planck Institute of Quantum Optics, has now realized an optical version of Schrödinger’s thought experiment in the laboratory. In this instance, pulses of laser light play the role of the cat. The insights gained from the project open up new prospects for enhanced control of optical states, that can in the future be used for quantum communications.

“According to Schrödinger‘s idea, it is possible for a microscopic particle, such as a single atom, to exist in two different states at once. This is called a superposition. Moreover, when such a particle interacts with a macroscopic object, they can become ‘entangled’, and the macroscopic object may end up in a superposition state. Schrödinger proposed the example of a cat, which can be both dead and alive, depending on whether or not a radioactive atom has decayed – a notion which is in obvious conflict with our everyday experience,” Professor Rempe explains.

In order to realize this philosophical gedanken experiment in the laboratory, physicists have turned to various model systems. The one implemented in this instance follows a scheme proposed by the theoreticians Wang and Duan in 2005. Here, the superposition of two states of an optical pulse serves as the cat. The experimental techniques required to implement this proposal – in particular an optical resonator – have been developed in Rempe’s group over the past few years.

A test for the scope of quantum mechanics

The researchers involved in the project were initially skeptical as to whether it would be possible to generate and reliably detect such quantum mechanically entangled cat states with the available technology. The major difficulty lay in the need to minimize optical losses in their experiment. Once this was achieved, all measurements were found to confirm Schrödinger’s prediction. The experiment allows scientists to explore the scope of the application of quantum mechanics and to develop new techniques for quantum communication.

The laboratory at the Max Planck Institute in Garching is equipped with all the tools necessary to perform state-of-the-art experiments in quantum optics. A vacuum chamber and high-precision lasers are used to isolate a single atom and manipulate its state. At the core of the set-up is an optical resonator, consisting of two mirrors separated by a slit only 0.5 mm wide, where an atom can be trapped. A laser pulse is fed into the resonator and reflected,  thereby interacting with the atom. As a result, the reflected light gets entangled with the atom. By performing a suitable measurement on the atom, the optical pulse can be prepared in a superposition state, just like that of Schrödinger’s cat. One special feature of the experiment is that the entangled states can be generated deterministically. In other words, a cat state is produced in every trial.

“We have succeeded in generating flying optical cat states, and demonstrated that they behave in accordance with the predictions of quantum mechanics. These findings prove that our method for creating cat states works, and allowed us to explore the essential parameters,” says Ph.D. student Stephan Welte.

A whole zoo of states for future quantum communication

“In our experimental setup, we have succeeded not only in creating one specific cat state but arbitrarily many such states with different superposition phases – a whole zoo, so to speak. This capability could in the future be utilized to encode quantum information,” adds Bastian Hacker.

“Schrödinger‘s cat was originally enclosed in a box to avoid any interaction with the environment. Our optical cat states are not enclosed in a box. They propagate freely in space. Yet they remain isolated from the environment and retain their properties over long distances. In the future we could use this technology to construct quantum networks, in which flying optical cat states transmit information,” says Gerhard Rempe. This underlines the significance of his group’s latest achievement.

Reference: “Deterministic creation of entangled atom-light Schrödinger-cat states”  by Bastian Hacker, Stephan Welte, Severin Daiss, Armin Shaukat, Stephan Ritter, Lin Li and Gerhard Rempe, 14 January 2019, Nature Photonics.
DOI: 10.1038/s41566-018-0339-5

2 Comments on "Scientists Realize Optical Version of Schrödinger’s Thought Experiment"

  1. Schrodinger’s cat is a direct conclusion from the assumption that the wave property in the particle-wave duality be the wave of probability. Because of the probability existing everywhere in the universe, a particle could appear everywhere no matter how far the location was. It is indeed difficult to verify the phenomenon experimentally because every measurement would interrupt the wave function. Therefore, the argument is going on and on without definite conclusions.

    But now we have found that Einstein’s relativity theory is completely wrong (see peer-reviewed publications: and ). The fatal mistake is that Einstein used Lorentz Transformation to redefine time and space and the newly defined time is no longer the physical time we measure with physical clocks. We know the physical time shown on any physical clock is T = tf/k where t is the theoretical time, f is the frequency of the clock and k is a reference frame independent calibration constant. In Newton’s mechanics, f is a reference frame independent constant too. Therefore, we can set k = f to make the clock show the theoretical time i.e. the absolute Galilean time: T = tf/k = tf/f = t.

    But in special relativity, frequency is a reference frame dependent variable and can’t be eliminated by setting k = f, thus, T can never be relativistic time t: T = tf/k != t. Therefore, relativistic time is never the clock time i.e. the physical time. On the other hand, when a clock is observed in another inertial reference frame, we have t’ = γt and f’ = f/γ and T’ = t’f’/k = γt(f/γ)/k = tf/k = T, which means that clock time won’t change with the change of the inertial reference frame, Lorentz invariant and absolute. That is, a clock still measures the absolute time in special relativity. As relativistic time is not the physical time we measure with physical clocks, special relativity is wrong.

    The fact that physical time (i.e. clock time) is absolute has been clearly confirmed by the clocks on the GPS satellites which are synchronized not only relative to the ground clocks but also relative to each other to show the same absolute time and directly denies the claim of special relativity that clocks can never be synchronized relative to more than one inertial reference frame no matter how you correct them.

    On the other hand, the fact that the speed of light can recover after going through a lens unlike the speed of a bullet which can never recover after going through a wall tells us that light is not particles but waves of some medium we call aether. The Michelson-Morley experiment tells us that aether is not a rigid medium but a fluid. The disproof of relativity tells us that the speed of light is isotropic only relative to the inertial reference frame moving with its medium aether.

    As light can exist everywhere in the visible part of the universe, aether must exist everywhere in the visible part of the universe too. Since light is “electromagnetic” phenomenon, aether must be the medium delivering all “electromagnetic” forces. Therefore, “electromagnetic” phenomena are just the phenomena of aether dynamics, and there is no such thing called “electric” field in nature, there is no such thing called “magnetic” field either. These “fields” are just lump sum macro effects of special flow patterns of aether.

    As aether exists everywhere in nature and plays critically important roles in all physical phenomena in the visible part of the universe, quantum mechanics should be wrong too because it has not taken the effects of aether into account. It look clear now that the biggest mistake in modern physics is the denial of the existence of aether.

    With aether, we know that the motion of a particle disturbs its surround aether to form waves. Therefore, the waves of aether are accompanying the motion of all particles, and the wave in the particle-wave duality should be the wave of aether rather than the wave of probability which is just a mathematical concept not a physical substance and can’t vibrate to form waves. Once the wave of probability is removed from modern physics, then there are no weird conclusions any longer: Schrodinger’s cat, quantum entanglement, etc.

    With the existence of aether, we can also easily understand that:

    * the extra gravitation binding stars in galaxies is provided by the mass of aether, not mysterious “dark matter”

    * the accelerating motion of galaxies away from each other is the result of pressure of aether just like the initial stage in the explosion of a bomb, not the mysterious “dark energy”

    * the bending of light near massive celestial objects is caused by the aether density change compressed by the gravitation of the celestial objects

    * Cherenkov radiation is the shockwave of aether generated by a local superluminal particle, just like the shockwave in the air generated by a local supersonic bullet

    * the slow rotation of the surface of the sun is the result of the drag of aether surrounding the sun

    With the existence of aether, we have found that everything is understandable without any weird concept.

  2. Is it possible to examine the time duration of an impression of an observation? When a random number of observers glimpse or view an image, their retention rate of the details and the image itself will vary widely over time. Is there any way to test the extreme mental condition of a rare number of people who view an image and have a difficult time forgetting its details, a form of photographic memory? What, you may ask, does this have to do with Schrödinger’s cat experiment, or the math and thought theories about it. From a psychological point of view, at the scale of electrons and atomic particles, any observation would have a different property than our ability to observe and capture a mirrored mental impression of the exact details of the particle. A mirror image of anything in everyday life is a series of points, but most of us observe real wholes of things, not clouds of their atomic particles. But assume that we could observe only the points of things as clouds of quanta. Instead of a cat, that is, you see only the quantum cloud of the cat’s electrons. And you yourself, of course, would have to be something of a quantum cloud, or at the atomic particle level. Then, on a one-to-one particle level, you would view the other particle as everywhere, and never see the cat that you would as a person. You would need a very complex formula in a Differential Calculus to describe how to travel from a particle to particle electron buried in a cloud observation to the point of electrons to the image of the cat outside the cloud of its particles. But the way our mathematical language for both types of observations may be confusing us, like using Roman numerals to approximate decimal numbers and fractions. So we may need to invent a different kind of mathematical language to describe the unified reality of quantum mechanics at the magnitudes of celestial cloud behavior of the cosmos.

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