Quantum Entanglement Just Got a Lot Stranger
The Quantum World Is Weird, and Now It Seems Even Crazier Than We Thought
Our brains evolved to understand a narrow slice of the universe, and anything outside of this slice seems bizarre. We intuitively grasp the flight of a spear, a running gazelle, or about how long it should take to cross the mountains and return home. All of these were needed to survive in our particular environment and in our particular slice. But something like a galaxy warping spacetime, light behaving as both a particle and a wave, or the behavior of quarks might snap our brains in half if we think about it too long. We simply don’t interact with the universe on those scales.
Easily among the weirdest known phenomena in the universe, quantum entanglement is so counterintuitive that Einstein called it “spooky.” In March 1947, Einstein wrote to his friend and colleague Max Born about the emerging field of quantum mechanics, and in this now famous letter, he expressed his doubt about quantum entanglement, even though this idea was based on his own work done in the 1930s. The main problems were that it seemed to violate basic principles of physics called causality and locality.
- Causality is the physical connection between cause and effect. The effect must happen after the cause, of course, and the effect cannot happen faster than is allowable by the speed of light, as Einstein proved. For example, when a photon leaves the Sun, it cannot excite an electron here on Earth before the roughly 8 minutes it takes to traverse the 93 million miles between the two.
- Locality is the idea that an object, whether on the macro- or micro-scale, can only be influenced by its immediate surroundings and that something must be the agent of influence. For example, a photon from the Sun cannot excite an electron on Earth until it directly interacts with it.
Quantum entanglement, on the other hand, seems to violate causality and locality.
“I cannot seriously believe in it because the theory cannot be reconciled with the idea that physics should represent a reality in time and space, free from spooky action at a distance.”
Albert Einstein
Quantum Mechanics and Wave Function Collapse
Quantum mechanics is all about the wave function, a mathematical description of a quantum system, such as a particle’s location, energy, and momentum. For example, an electron in a box with impermeable boundaries has certain probabilities of being at different locations when measured based on its possible energy levels. However, unlike classical physics, this electron is both present and not present at all of these locations before being measured. It is not until it is measured that it is forced to “choose.” At this point, the wave function collapses into a discrete value, as opposed to a range of probable values.
Now consider Schrödinger’s cat. In this thought experiment, a cat is confined in a box, and its fate is tied to the state of a quantum particle. The presence of this particle in a certain part of an impenetrable box will trigger the release of cyanide gas, killing the cat. However, the quantum particle is both present and not present, as its wave function has yet to collapse, meaning the cat is both dead and alive. Of course, this seems absurd, and Schrödinger himself agreed because macro-scale objects like a defenseless animal trapped in a box do not exhibit quantum phenomena. On the quantum-scale, though, these phenomena have been repeatedly demonstrated.
In the famous double-slit experiment, a beam of light, for example, acts like a wave as it passes through the two slits. The constituent photons spread out according to all the probable locations. However, when a conscious observer detects which slit a photon went through, it behaves like a particle, as its wave of probability collapses. That is, instead of existing at all probable locations, it is forced to choose one. The act of measuring the photons changed them from behaving as a wave to behaving like solid particles.
Quantum Entanglement, the Basics
In the 1930s, physicists, including Erwin Schrödinger and Einstein, stumbled upon the idea of quantum entanglement and were naturally confused. It seemed to imply a violation of locality and causality because of faster than light communication, which Einstein had just proven impossible with his Theory of Relativity. So Einstein and two colleagues, Podolsky and Rosen, set out to solve the riddle, creating what is now known as the EPR paradox. This was a thought experiment that seemingly demonstrated quantum mechanics was incomplete and that “hidden variables” must be present. When these extra variables were accounted for, the mystery of quantum entanglement disappeared. In particular, the principles of locality and causality were restored.
EPR was heavily debated for decades, with famous physicists like Neils Bohr finding fault with it, and it was not until after Einstein’s death that it was finally disproved. John Stewart Bell successfully demonstrated that not only do hidden variables not exist but that they are inconsistent with the principles of quantum mechanics. That is, he reaffirmed the craziness that is quantum entanglement.
So this is how quantum entanglement works.
- A pair of particles is created or two particles interact.
- The particles naturally take on opposite values, such as positive/negative or clockwise/anti-clockwise spin.
- The particles hold these values after being separated, assuming they are kept in isolation.
- The state of the two particles is not known until measured.
- Measuring the state of one particle collapses the wave function for both particles.
One of the craziest parts of quantum entanglement is that distance doesn’t matter. The entangled particles can be right next to each other, on the other side of the planet, or theoretically on the other side of the universe. Regardless of how far apart they are, when one particle is measured and its wave function collapses, the other’s wave function also instantaneously collapses into an opposite value. Seemingly, this implies some sort of connection that isn’t affected by distance or time.
The Quantum Plot Thickens
While the above is certainly brain-snapping enough, things just got stranger. In 2008, Dr. Hotta from Tohoku University in Japan published a paper in which he created a protocol to transfer energy between entangled particles. In simple terms, he explained that Alice excites one of the entangled particles by performing a measurement on it, which causes wave packets of positive energy to propagate outwards. At this point, she tells Bob via classical communication to make a non-invasive measurement of the other particle. Bob should see negative energy wave packets propagating outward that are exactly opposite the energy gain seen by Alice. Hotta claimed that quantum entanglement could be used to charge the energy of one particle and discharge the energy of the other.
“The negative-energy wave packets begin to chase after the positive-energy wave packets generated by Alice.”
Dr. Masahiro Hotta, 2008
Hotta followed this idea a few years later with another paper in which demonstrated the protocols for quantum energy teleportation. These protocols were far more detailed and had a stronger mathematical foundation. In this paper, he showed it was theoretically possible to transport quantum energy from one many-bodied subsystem of quantum particles to another.
“These relations help us to gain a profound understanding of entanglement itself as a physical resource by relating entanglement to energy as an evident physical resource.”
Dr. Masahiro Hotta, 2010
Dr. Hotta didn’t get the experimental proof of his ideas until March, 2022. In a paper published on arXiv, authors Rodríguez-Briones, Katiyar, Laflamme, and Martín-Martínez used magnetic resonance, the same used in an MRI machine, to finely tweak the energy levels of an entangled particle. As Dr. Hotta predicted, the other entangled particle showed an equivalent loss of energy.
“We report the first experimental realization of both the activation of a strong local passive state and the demonstration of a quantum energy teleportation protocol by using nuclear magnetic resonance on a bipartite quantum system.”
Rodríguez-Briones, Katiyar, Laflamme, and Martín-Martínez
Further evidence came in January, 2023. Physicist and computer scientist Kazuki Ikeda used quantum computers to also show energy transfer between entangled particles. By using a handful of IBM’s superconducting quantum computers, Ikeda and colleagues believe they have not only demonstrated the possibility to transfer quantum energy but opened the door for a quantum computing revolution.
“The ability to transfer quantum energy over long distances will bring about a new revolution in quantum communication technology.”
Kazuki Ikeda
Quantum Mysticism, Preserving Causality and Locality
Quantum entanglement and other quantum effects are hot topics among New Age spiritualists. They want to believe that quantum effects prove a deeper, inexplicable connection between people, nature, the universe, or the subconscious mind. Perhaps the most famous example is Deepak Chopra’s book “Quantum Healing,” in which he attempts to explain his theory of mind and body with help from quantum mechanics. Unfortunately for his readers and others wasting their time and money with quantum quackery, these ideas are based on misunderstandings.
In particular, though it was originally thought to violate locality and causality, quantum entanglement does not enable faster than light communication of any sort. On the surface, it seems like it would be possible to send some type of signal with the following setup:
- You entangle two particles.
- You separate the entangled particles by an extremely long distance, making sure to keep them isolated.
- You stay with one particle and make a measurement, forcing it to choose a state.
- The other particle is then forced into the opposite state.
- Another observer with the other particle would then be able to tell that you have made a measurement.
This would be transferring information faster than the speed of light, right? Well, no. The problem is that the act of measurement breaks the entanglement. When the distant observer goes to measure their particle, they’d find that the original measurement had no effect. In the many experiments proving quantum entanglement, the particles are not measured by observers. For example, the first of these experiments was performed by Clauser and Freedman. In 1972, they entangled two photons and then sent them in opposite directions towards a set of polarization filters. Whether or not they passed through these filters depended on their polarizations. Clauser and Freedman found that their likelihood of passing through were highly coordinated, far above random had they not been entangled. However, had they measured the particles before or during the experiment, they wouldn’t have preserved the entanglement.
What about Dr. Hotta’s quantum energy transfer? Yes, his models and the subsequent experiments demonstrate quantum energy transfer through entanglement, but this doesn’t happen faster than the speed of light. In fact, such an energy transfer would normally take around a second to happen, but in the experiment the energy transfer between entangled particles only took around 37ms, about 20 times faster.
Therefore, both causality and locality are not being violated with quantum entanglement, as faster than light communication is not possible. Quantum quackery, then, is either a scam or being pushed by, in the nicest terms possible, well-meaning but misinformed individuals. The quantum world is already magical enough without the addition of such nonsense.
