Chapter 1: The Concept of Quantum Teleportation

Have we reached a point in technology where we can strap on our communicators and expect to experience something akin to teleportation?

In the summer of 2017, numerous reports from popular science publications excitedly announced that Chinese scientists had achieved quantum teleportation between a ground station and a satellite. For many, this evoked images reminiscent of Star Trek. Does this mean we are on the brink of a reality filled with matter transporters and instantaneous communication, transcending the light-speed barrier established by General Relativity?

The short answer is no.

The term "teleportation" can be quite misleading. In science fiction, it suggests the disassembly of atoms in one location and their reassembly elsewhere, all in a flash. This concept originated from the need for a narrative device in television, as special effects were often too costly. The idea of transporting matter has captivated audiences ever since. However, when scientists refer to teleportation, they mean something entirely different.

They are discussing the instantaneous alteration of quantum states in two entangled particles, irrespective of the distance between them. But how can this occur when all evidence indicates that nothing can surpass the speed of light, which travels at roughly 300,000 kilometers per second?

This phenomenon is explained by quantum entanglement. When particles are entangled, they form a single system; thus, a change in one particle causes an immediate corresponding change in the other. This change occurs instantaneously—a notion that frustrated Einstein, who derisively termed it "spooky action at a distance." Since the validation of quantum entanglement, there has been interest in harnessing it for instantaneous communication beyond light-speed constraints.

At this point, it's essential to clarify that physicists use "teleportation" in a manner distinct from its popular interpretation. It’s akin to two telephones linked by an extensive wire (or, in modern terms, the global telecommunications network). When Mary speaks to Bob on the phone, the device doesn't vanish from her hand and reappear in Bob's; similarly, physicists' teleportation does not involve physical disassembly and reassembly. Instead, it denotes that two entities can instantaneously affect one another over a distance.

So, if we can't achieve Star Trek-like effects, could we at least have a form of subspace communication that would allow a starship captain to order pizza from light-years away without waiting years for a response?

Unfortunately, the answer remains no, but the reasons extend beyond mere terminology.

To understand why quantum entanglement does not facilitate instantaneous communication, let’s examine the mechanics involved. The Chinese experiment initiated quantum entanglement by entangling photons. A photon, as a massless entity, travels at light speed, existing as both a particle and a wave. Photons propagate as intertwined electric and magnetic waves, which is why polarized filters work: light oscillating in alignment with the filter passes through, while light oscillating in the opposite plane is blocked.

To create a pair of entangled photons, one can direct a photon through a specialized prism that divides it into two identical photons, each possessing half the frequency of the original. Consequently, any change to one photon will instantaneously affect the other.

In the Chinese experiment, a photon was split to form an entangled pair; one photon was sent to a satellite while the other remained on the ground. The scientists entangled the ground photon with another and measured the quantum states (polarizations) of this new combination. However, the term "measured" is crucial here. There are four potential quantum states for this new pair: vertical-vertical, vertical-horizontal, horizontal-vertical, and horizontal-horizontal. The researchers could only determine whether the states matched or differed.

Due to entanglement, the satellite photon must correspond to half of whatever state the lab photon was in. However, unless the satellite's photon was informed of the ground state, it could not ascertain this by measurement alone—there are simply too many variables involved. The best the satellite could achieve would be to identify two of the four states, which wouldn't allow for effective communication.

The core of quantum entanglement is that comprehensive knowledge of the entire system is necessary to describe it fully. Measuring just one part is insufficient. Therefore, while it is true that a pair of entangled photons may probabilistically mimic each other across great distances, measuring one alone does not provide complete insight into the entangled system.

To illustrate, consider Bob mixing two paint colors—orange and blue—creating brown. If he sends Mary a brown sample, she cannot determine if it originated from orange and blue or red and green without additional information. This analogy underscores the difference between mere transmission and meaningful information.

Let's compare it to walkie-talkies, which transmit signals via radio waves. If atmospheric interference distorts the waves significantly, the receiver may hear static but discern no actual information. The satellite receives an entangled photon as a transmission, yet it cannot convey any information. It can only signal its presence, but the intended message remains inaccessible until conventional communication occurs between the lab and the satellite.

This dynamic presents a classic chicken-and-egg dilemma. Regardless of how many entangled photons reach the satellite, each suffers from the same issue: while the signal is detectable, no information can be extracted until the lab sends information via conventional means, which is limited to light-speed transmission.

This limitation is precisely why quantum entanglement cannot facilitate faster-than-light communication.

Additionally, many textbooks and popular science articles depict quantum phenomena as deterministic, akin to classical mechanics, which is misleading. A pertinent example is the double-slit experiment, where individual particles are aimed at a detector through two small slits. Each photon can pass through one slit or the other, yet the interference pattern emerges only after many particles have been fired. The location of any single particle hitting the detector provides no predictive insight into the next particle's position. Quantum mechanics operates on probabilities; thus, the state of any individual particle remains uncertain.

So, why did the Chinese scientists pursue this experiment? The primary advantage of quantum entanglement is its potential for secure communication. If a message is sent via entangled photons, and subsequent conventional information is shared about the entangled pair, the recipient can measure the photons and verify their states. If they match, the message remains secure; if not, it indicates interception.

However, Mary must receive this conventional signal promptly, as measurement alters the entangled state irreversibly. If she measures before Bob sends a message, the entanglement will be lost. Thus, she cannot know when the message is being sent unless informed through classical means.

Ultimately, what the Chinese demonstrated was not sci-fi magic but rather the potential of entanglement to safeguard information flows. Any interception alters the photons, revealing that the message was compromised, but only if the proper conventional communication is established.

This application of entanglement may prove valuable, but we are far from stepping onto transporter pads or engaging in subspace radio communication. So, there’s no need to dust off those old Trekkie costumes just yet.

Chapter 2: Quantum Communication: Security over Speed

To further explore the nuances of quantum teleportation, we turn our attention to additional resources.

The first video, titled "Transporters and Quantum Teleportation," delves into the intersection of science fiction and the realities of quantum mechanics, emphasizing the differences between popular perceptions and scientific facts.

The second video, "Quantum Teleportation Demystified with a Quantum Computer | Paradoxes Ep. 08," provides an in-depth look at the principles of quantum teleportation and its implications for the future of technology and communication.