The macroscopic object is almost transferred to a quantum state – is there a human next in line?

The macroscopic object is almost transferred to a quantum state - is there a human next in line?

Fig. one. The laws of the quantum world seem strange and incomprehensible to most of us – the inhabitants of the macrocosm. Quantum objects, for example, simultaneously exhibit the properties of both particles and waves, can be in a superposition of several completely different states, and also allow mutual entanglement, as a result of which they acquire the ability to instantly “feel” each other at any distance. Scientists are already accustomed to working with such things and are trying to take quantum experiments to a new – macroscopic – level. Drawing from britannica.com

The laws of the quantum world seem paradoxical to us only because we, non-quantum thinking observers, are forced to look at this world from the outside. But what if you transfer the person himself to a certain quantum state and give him the opportunity to look at the quantum world from the inside? What will he feel and realize? The answers to these questions, despite their fantastic nature, can be obtained in the near future. A recent article appearing in the Preprint Archive reports a revolutionary achievement – the translation of a 10 kg macroscopic body into an almost pure quantum state. One more leap – and this technology will allow transferring a whole person into a certain quantum state. It is possible that sessions of full immersion in the quantum world will become entertainment for the general public during our lifetime.

The laws of quantum mechanics seem to us very unusual, even paradoxical. But this is only because we, macroscopic non-quantum observers, do not ourselves participate in the “quantum game” of the universe. We look at it as if from the outside and try to comprehend it logically, and not through sensations.

For theoretical physicists, there is also a subject for heated debate here, although of a somewhat different nature. Of course, from a computational point of view, this is not a problem. Physicists have already become accustomed to the laws of the microworld, know how to express them mathematically and know how to calculate the probabilities of certain quantum processes. But this is all applicable only as long as we describe individual atoms and molecules. Macroscopic objects, on the other hand, have no trace of quantum behavior. The intrigue here is that in the very structure of quantum mechanics there is no hint of the limits of its applicability. In theory, quantum mechanics should work in general for all objects, including the entire universe. How is it that we are losing the quantum thread in the everyday world? Alas, it is not known. Despite the centuries-old history of disputes among physicists, there is still no generally accepted theory that would explain this transition from quantum to classical in every detail.

Perhaps, the hottest battles are caused by the postulate that human consciousness itself influences the evolution of quantum systems and thereby determines this or that development of events in the surrounding world. Some physicists see this as a solution to all the conceptual paradoxes of quantum mechanics. The modern version of this school of quantum thought is called Bayesian Cubism (QBism); some idea of ​​it can be obtained from the article An Introduction to QBism with an Application to the Locality of Quantum Mechanics. Other researchers either categorically reject such speculations, or believe that they are outside the scope of science.

While theorists and philosophers argue about what is actually happening on the blurred border between the quantum and the classical, experimenters began to probe this border experimentally. For example, in 2009, scientists were able to transfer into a state of quantum superposition not a single molecule, but a whole virus (see details in the popular article Quantum diseases can threaten Humanity). Over the past decade, technology has steadily evolved, fueled by a wide variety of projects in the field of fundamental physics. And in 2021, researchers managed to come close to converting a truly macroscopic object weighing 10 kilograms into a pure quantum state!

This impressive achievement is described in the publication Approaching the motional ground state of a 10 kg object, which has appeared so far in the form of an electronic preprint and sent to the journal. The article was signed by two hundred authors, most of them working at the LIGO gravitational-wave observatory. And this is not accidental: after all, the massive mirrors of the gravitational-wave antenna played the role of a 10-kilogram object, which the authors managed to cool almost to a pure quantum state.

Fig.  2. One of the massive mirrors of the LIGO gravitational-wave antenna

Fig. 2. One of the massive mirrors of the LIGO gravitational-wave antenna. Photo from the site ligo.caltech.edu

Why is an ordinary macroscopic object, even if it is a simple piece of polished crystal, so far from the quantum world? Because it is at a sufficiently high temperature and continuously interacts with the environment. Molecules vibrate inside a solid, and if these vibrations were not enough, then the external environment will swing them due to collisions with gas molecules or thermal radiation. But the mirrors in LIGO are suspended in vacuum on complex suspensions and are maximally isolated from the external environment. If you cool them, completely suppressing any movement inside, then the massive mirror will be in a pure quantum state and you can work with it like a quantum particle of a huge mass.

All this, of course, is very difficult. But the LIGO technology was precisely designed to achieve what seemed previously unattainable (here’s a practical application of the search for gravitational waves!). The researchers report that they were able to stop almost all molecular movement inside the mirrors. According to their estimates, about a dozen phonons remained in massive mirrors – quanta of crystal lattice vibrations – which corresponds to a temperature of less than 100 nanokelvin. The authors are confident that in third-generation gravitational-wave antennas, the motion will be eliminated completely, reducing purely phonons to one, and even then arising only from time to time. This will be a truly basic quantum state of translational motion for a record-breaking object.

But since it is possible to cool a heavy crystal to a pure quantum state, why not do this with a person as well? After being transferred to a pure quantum state, a person will begin to evolve in accordance with the laws of quantum mechanics and become a full-fledged part of the quantum world! This means that a dizzying prospect opens up to feel the paradoxes of the quantum world on oneself and then tell what it is like. It will finally be possible to experimentally test how human consciousness affects quantum superposition!

The journey of a person through the quantum world can be controlled as we control atoms. This will be most conveniently done using the so-called entangled states of the object under study with a quantum manipulator. Until recently, entangled states were observed only for individual elementary particles or atoms. However, last year the first results on entangling of quantum states of macroscopic objects appeared (S. Kotler et al., 2020. Tomography of Entangled Macroscopic Mechanical Objects). The objects there were not so big: not massive crystals, but rather grains of sand. But this is only the beginning, and one can expect that one day quantum entangled states of the same mirrors in gravitational wave antennas will be realized.

Thanks to external control, a traveler in the quantum world can be transferred to a superposition of states (analogue of Schrödinger’s cat) or to a delocalized state when he is simultaneously there and here. It will even be possible to confuse the state of the two volunteers by conducting quantum wedding ceremonies, as well as organize sessions of collective entanglement. In short, the most exciting prospects are opening up.

Of course, on the way to immersion in quantum reality, there are still many technical difficulties to overcome. The person will have to enter the quantum hibernation mode, which is a very promising, although still not studied, medical problem – after all, the quantum state will successfully replace anesthesia during surgery. It will also need to develop a new ethical protocol for the journey into the quantum world. But you can be sure that there will be volunteers for such a noble goal, just as they are for a one-way flight to Mars.

Well, then, after the stories of the pioneers, a crowd of quantum tourists, thrill-seekers and other quantum tiktokers will undoubtedly rush into the reality next to us, but hidden from everyday life. And who knows, maybe in one generation, quantum entanglement and delocalized state will become the usual leisure time for young people.

A source: Chris Whittle et al. Approaching the motional ground state of a 10 kg object // arXiv preprint: 2102.12665 [quant-ph]…

See also:

Shlomi Kotler et al. Tomography of Entangled Macroscopic Mechanical Objects // arXiv preprint: 2004.05515 [quant-ph]…

Igor Ivanov

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