Dr Mažena Mackoit-Sinkevičienė: What Do Cats and Teleportation Have in Common?
Quantum physics, with its mysterious phenomena, raises more and more questions about the nature of reality – from Schrödinger’s cat, which is both alive and dead at the same time, to quantum teleportation that transmits quantum states without transferring any physical matter. Schrödinger’s cat – the most famous thought experiment in quantum physics and probably the most well-known cat in the history of science – has long been more than just a topic of scientific debate. It has become a symbol of everything that lies beyond the limits of ordinary perception. Just as the quantum cat challenged us to rethink the very nature of reality, quantum teleportation prompts us to reconsider the essence of information and how it can be transmitted with even greater precision.
The precision of quantum physics is a miracle unfolding every day
Quantum theory is a mysterious yet remarkably precise science that describes the behaviour of the smallest particles in the universe: electrons, atoms, molecules, and photons. Its precision is so astonishing that renowned physicist Richard Feynman once compared it to measuring the distance between New York and Los Angeles with an accuracy equal to the width of a human hair. To illustrate this with a Lithuanian example: if we could measure the distance between Vilnius and Klaipėda with the accuracy of a single page from ‘Catechism’ by Martynas Mažvydas, quantum physics would still be a hundred times more precise.
Yet quantum phenomena are not just confined to laboratories – they constantly occur all around us. Any interaction between matter, whether with other matter or light, is, at its core, a quantum process. All electronic devices rely on quantum phenomena, and even the Sun could not exist without quantum forces that allow hydrogen atoms to fuse and release energy. Quantum phenomena also drive certain biological processes, such as photosynthesis, which allows plants to generate energy from light and direct it efficiently to specific cells in the appropriate part of the plant.
Teleportation is about information transfer, not cloning
When asked about teleportation, most people probably imagine movie scenes where an object or person is broken down into a set of atoms and its entire scheme is transferred to another place before being reassembled from atoms at the destination. Although such an idea might sound intriguing, it contradicts quantum physics, which claims that we cannot extract all the information about a particular system because it is impossible to create an independent and identical copy of an arbitrary unknown quantum state.
According to the no-cloning theorem, it is impossible to create an exact copy of the quantum state of even a single particle.This means we cannot simply duplicate a person or any other system in a quantum state because determining the information of a quantum state requires measurement. This action irreversibly destroys the quantum superposition and creates only one of the possible outcomes. As in the case of Schrödinger’s cat, it cannot be both alive and dead at the same time. So, even when it comes to genetic cloning, scientists point out that processes such as the cloning of Dolly the Sheep are based on biological principles rather than precise atomic replication. If a cloned sheep lacked a few strands of wool, it would be imperceptible in biological terms, but in physics, this would mean that some atoms are lost, and the clone would not be completely identical to the original.
How does a bird’s inner compass work?
In reality, human teleportation would be impractical due to the sheer number of atoms involved (an average person weighing 70 kg has nearly 7×1027 atoms, i.e. seven billion billion billion), so teleportation has a different meaning in quantum physics. Here, it refers not to the transfer of matter but to the transmission of information, made possible by quantum entanglement – a phenomenon occurring at the level of elementary particles.
Quantum teleportation is a method for transferring a quantum state from one particle to another without physically moving the particle itself. This is one of the most fascinating aspects of quantum mechanics: two or more quantum objects can behave in exactly the same way (like identical twins) because they share encoded information, even when separated by vast cosmic distances. When one is disturbed, the other changes instantly as well, no matter how far apart they are. All this happens due to the invisible link, known as entanglement. Whatever we call it, the process transfers the quantum state of one particle to another identical one, simultaneously destroying the original state in the process. What makes it especially remarkable is that it works even if you do not know what kind of ‘information’ you are sending, i.e. what the quantum state of the original particle is. This is especially important because trying to measure an unknown quantum signal can disrupt and alter it.
It is no surprise that Albert Einstein opposed the idea of entanglement back in 1930 – at that time, it was impossible to verify this phenomenon experimentally. However, this became feasible in the 1970s. Since then, numerous successful entanglement experiments have been conducted (in 2023, CERN managed to observe quantum entanglement between a top quark and its antimatter counterpart). Physicists Alain Aspect, John F. Clauser, and Anton Zeilinger – each working independently and refining their own methods – demonstrated that it is not only possible to study entangled particles, but also to control them (which earned them the Nobel Prize in Physics in 2022). This phenomenon holds tremendous potential for advancing communication technologies and strengthening national security.
Quantum entanglement is not just a theoretical miracle of science but also an important natural phenomenon that helps birds migrate and orient themselves in the Earth’s magnetic field. A special protein found in birds’ retinas, called cryptochrome, acts as an internal compass. This light-sensitive protein allows birds to detect the Earth’s magnetic field. When light enters a bird’s eyes, it excites the cryptochrome molecules, creating a pair of entangled electrons. These electrons are highly sensitive to even the slightest changes in the magnetic field, enabling birds to determine their geographical position and direction of travel. This example from nature highlights the relevance of quantum phenomena and how they can influence living systems. However, quantum phenomena are not limited to small objects – researchers at the Delft University of Technology have demonstrated that quantum teleportation can also be applied to larger structures, such as optomechanical devices composed of tens of billions of atoms.
Quantum communication is more accurate than classical means of communication
Teleportation has already become a reality, and recent successful quantum teleportation experiments are capturing growing public interest. Teleportation enables the transfer of quantum information in the form of quantum states from one location to another, thereby forming a quantum network. This process relies on quantum entanglement and the classical means of communication. Although it is a complex technology that began with early laboratory experiments (Zeilinger was the first to demonstrate quantum teleportation in 1997), we are now starting to see its practical demonstrations. The first results showing that quantum and classical networks can share the same fibre-optic infrastructure were achieved only a few months ago, on 20 December 2024. All telecommunications technology (including the internet) depends on the transmission of light particles (photons) through optical fibres. In optical communication, digital data signals are converted into light and transmitted over long distances through fibre optics. This is a key element of most telecommunications systems. Although the classical connection consists of millions of light particles, quantum communication uses only individual pairs of photons, i.e. quantum light.
Previously, scientists believed that these two light particles would not be able to pass through a crowded ‘highway’ of classical communication particles, as they would be like a fragile bicycle trying to weave its way through massive trucks in an underground tunnel. So, researchers had to find a solution to guide these delicate particles. Light consists of waves of different lengths, and scientists have identified a specific wavelength where less interference with other signals is experienced, making it easier for photons to move around. Interference is like two radio stations playing simultaneously: if their waves align, the sound gets louder, but if they clash, the sound becomes chaotic or disappears altogether. Researchers selected individual photons at a specific wavelength and added special filters to reduce the noise caused by ordinary internet traffic.
A recent study has demonstrated the potential for quantum teleportation in real-world conditions. For the experiment, a 30-km-long fibre-optic cable was set up, with a photon at each end. The cable simultaneously carried both regular internet traffic and quantum information. Despite the heavy internet traffic, the quality of quantum information at the end of the cable remained high. This discovery is highly significant and perfectly timed, especially as 2025 has been declared the International Year of Quantum Science and Technology.
But why is this breakthrough so significant? The key point is that quantum teleportation can now function over existing fibre-optic networks, eliminating the need to build entirely new infrastructure. This proves that classical and quantum communication can work together in harmony. The ability to use quantum teleportation in already existing optical fibre network systems not only paves the way for building next-generation quantum networks but also lays the foundation for advancing quantum communication to a whole new level.
Teleportation ensures secure communication
Imagine being able to hand over a secret note to a friend without anyone else being able to read it, even as the note was passed through a crowded room.
This is now becoming a reality with quantum encryption, one of the most practical applications of quantum teleportation. More than 140 years ago, American banker Frank Miller proposed an unbreakable cipher called a one-time pad, in which the sender and the receiver share keys consisting of random values. However, this method was not completely secure because such a key needed to be transmitted to both the sender and the recipient, making it vulnerable to interception. But quantum entanglement – the foundation of modern quantum teleportation – solves this problem by ensuring that the random values transmitted over long distances remain linked and cannot be intercepted.
Quantum teleportation makes this possible through quantum key distribution (QKD) systems, which guarantee that a connection is practically impenetrable to outsiders, so a third party cannot intercept or read the random key before the particles have reached their destination. In this way, quantum teleportation allows the secure transmission of quantum keys used in QKD protocols (e.g. BB84), effectively safeguarding communication channels against interception. In 2017, Chinese scientists tested this technology using the Micius satellite, sending entangled photons to two locations 1,200 km apart. This is a good example of what intercontinental quantum networks could look like in the future; they will be as important as the first phone call, which once revolutionised how we communicate.
Humanity’s most successful theory
Today, quantum teleportation is used not only for fundamental research in quantum physics, e.g. demonstrating entanglement and quantum non-locality, but also for transferring quantum states between different quantum processors. It is critical to enabling the transfer of quantum states between different quantum processors and is key to applying quantum advances in various fields, such as computing, cryptography, and sensing.
Quantum physics is considered one of the most successful theories ever developed by humanity; yet, it still raises profound questions. One of them is the measurement paradox: a quantum state with many possible outcomes changes when observed, and we get only one specific measurement result. This raises doubts about the role of observation and information in our lives and may eventually force us to rethink the difference between the observer and the observed.
Perhaps this will shed more light on the paradox of Schrödinger’s cat and quantum teleportation. Only time will tell.