Spin-State Teleportation and Tests of EPR Correlations Using 151 MeV Entangled Protons

In the subatomic world, particles like protons do not always behave as isolated individuals. Sometimes, two protons can become so deeply linked that they share a single quantum existence, a phenomenon known as entanglement. In this state, the properties of one particle, such as its spin or intrinsic angular momentum, are inextricably tied to the other, no matter how far apart they drift. This connection defies our everyday intuition about separate objects, yet it is a well-established feature of quantum mechanics. Scientists have long been interested in whether this strange link can be used to move information. Specifically, they have asked if the quantum state of one particle can be transferred to another without physically carrying the particle itself, a process called teleportation. While this concept has been demonstrated with light and atoms, testing it with protons—the heavy building blocks of atomic nuclei—presents a unique challenge. Protons are difficult to control at the precise energies and angles required to maintain their delicate quantum links, and previous attempts to do so were limited to very low speeds where the particles lose too much energy to be useful.

A researcher at the Jagiellonian University in Poland has now explored whether this quantum teleportation could work with protons moving at much higher speeds, specifically at an energy of 151 MeV. Their work, detailed in a recent study, investigates a complex three-proton system to see if the rules of quantum mechanics allow for the transfer of a proton's spin state under these more energetic conditions. The researcher found that while the high-energy environment changes the nature of the entanglement, it does not destroy the possibility of teleportation. However, achieving this requires a specific and somewhat counterintuitive setup. Unlike earlier experiments that relied on simple collisions between two protons, this new approach proposes that the entangled pair be created through the breakup of a deuteron—a heavy form of hydrogen nucleus—by a high-speed proton. This specific reaction, occurring under precise geometric conditions, is suggested to produce a pair of protons that are entangled in a way that allows one of them to interact with a target and transfer its quantum state to its partner.

The core of the experiment involves a sequence of events that begins with the creation of this entangled pair. The researcher proposes firing a beam of protons at a target containing deuterons. When a high-energy proton strikes a deuteron, it can cause the deuteron to break apart, releasing a neutron and two protons. By carefully selecting the angle and energy of the incoming beam, the scientist aims to ensure that the two outgoing protons are produced with equal momentum and are locked into a specific entangled state. In this state, the two protons are so strongly correlated that measuring the spin of one immediately reveals the spin of the other. The researcher then takes one of these entangled protons and scatter it off a second target made of polarized hydrogen, where the protons are aligned in a specific direction. The interaction between the flying proton and the target proton acts as the trigger for the teleportation process.

What the researcher discovered is that this interaction transfers the polarization, or spin orientation, of the target proton to the second member of the entangled pair, but this result is strictly valid only, or is best approximated, when the scattering occurs at a very specific angle, roughly 45 degrees in the laboratory frame. This happens even though the second proton never touches the target. The process works because the initial entanglement between the two flying protons is so strong that the change in the first proton's state is instantly reflected in the second. The study shows that for this transfer to be clean and effective, the scattering must occur at this specific angle. At this angle, the quantum mechanics of the collision simplify, allowing a single dominant interaction to take over, which ensures the teleportation is precise. If the angle deviates even slightly, the clarity of the transfer begins to blur, and the entanglement becomes contaminated by other effects.

The researcher also examined what happens if the target is not polarized, meaning the protons in the target are not aligned in any specific direction. In this scenario, they found that scattering one of the entangled protons off the target induces a polarization in that scattered proton. Due to the strong quantum link, this induced polarization is mirrored in the second, unscattered proton. The unscattered proton, which started with no polarization, suddenly acquires a spin orientation that matches the first proton, with its direction determined by the specific type of entanglement they shared. This finding offers a simpler way to test the famous Einstein-Podolsky-Rosen correlations, which describe these spooky connections, because it does not require the difficult-to-maintain polarized target used in the full teleportation setup.

However, the path to this result was not a straight line. The researcher had to rule out a more straightforward method that had been considered for high-energy experiments. They showed that simply colliding two protons at 151 MeV to create an entangled pair would not work for teleportation. In that standard collision, the two resulting protons would each have only half the energy of the incoming beam, dropping to about 75.5 MeV. At this lower energy, the quantum conditions required for the teleportation to occur are no longer present. The dominant interaction that makes teleportation possible disappears at 75.5 MeV, meaning the second step of the process would fail. This realization forced the researcher to abandon the simple two-proton collision idea and propose the more complex three-body breakup method, where the initial collision energy is high enough to produce the entangled pair at the correct 151 MeV energy level.

Through detailed numerical simulations using realistic models of how protons interact, the researcher confirmed that their proposed setup is theoretically sound. They calculated the final states of the protons and found that the polarization transfer is nearly perfect within the narrow window of angles where the entanglement is strongest. The simulations accounted for the complex forces between the protons, including the electrical repulsion they feel from each other, to ensure the predictions were accurate. The results indicate that the polarization of the target proton is faithfully transferred to the distant partner, with the sign of the polarization depending on the specific type of entangled state formed. This work suggests that while the technical hurdles are significant, the physics of quantum teleportation with protons at high energies is not only possible but follows a clear and predictable path.

The study concludes by highlighting that this high-energy approach offers a fresh perspective on testing the fundamental nature of quantum reality. By moving away from the low-energy regime where energy losses have been a major obstacle, the researcher has opened a new avenue for experimentation. The ability to generate and manipulate these entangled states at 151 MeV could lead to more robust tests of quantum mechanics, free from the limitations that have plagued previous attempts. While the experiment has not yet been performed in a laboratory, the theoretical groundwork laid by this paper provides a clear blueprint for what to expect. It demonstrates that the strange, non-local connections of the quantum world can be harnessed even in the high-energy environment of nuclear physics, provided the conditions are set with enough precision to let the dominant quantum interactions shine through.