Chicago now has a 12-mile quantum network. This is what it's for:  Earlier in June, 2022, a group of research labs in Chicago unveiled an extended 124-mile quantum network running from the suburb of Lemont, through the city of Chicago, to the Hyde Park neighborahood and back.     That total length accounts for a newly added, 35 mile-long segment of optical fiber that was recently connected to an 89-mile quantum loop that the U.S. Department of Energy's Argonne National Laboratory launched in 2020, linking labs from the Chicago Quantum Exchange and the University of Chicago.        The invention behind building such a network is to enable researchers to experiment with new types of quantum communications, security protocols, and algorythms with the goal of advancing towards a preliminary quantum internet (which could very well look like an early version of the classic internet).    Currently, Toshiba is using it to test their distributed quantum encryption keys-in a setting that experiences factors like noise, weather, and temperature fluctuations in order to understand how robust this method is, and what potential issues may come up.  The researchers have been able to send information so far at top speed of 80,000 quantum bits (or qubits) per second.               These kinds of experimental keys could be usefull in a future where powerful quantum computers threaten to break classical encryption, an issue that has been highlighted by lawmakers in Congress.    As bigger quantum computers began to emerge, researchers are actively exploring ways to use the law of quantum physics to establish a communication channel that would be tamper-proof and hack-proof. This type of communication channel could also become a method of "wiring" together quantum devices. "Let's say you have a quantum computer that's up to 1,000 qubits.  And here you have a second computer that's 1,000 qubits.  You'd like to wire them together in the same way we build supercomuters today by making clusters, but you can't wire the computers using classical wire.  You need a quantum wire to keep quantum states of both machines," says David Awschalom, a professor at the University of Chicago and a senior scientist at Argonne National Laboratory.   "So, a quantum communications channel is a way to do that-basically building a way for two quantum circuits to talk to one another without ever entering the classical world."    

Probing all the possibilities of Quantum Communications:  Because this is the quantum world, things work a little differently.  To start, for objects to exhibit quantum qualities, they have to either be very cold or very small.  Chicago chose small.  "Many of today's commercially available quantum machines are usually superconductors, so they have to have very low tempetures," says Awschalom. "Quantum communications use photons, and the polarization of the light encodes the information."  That means the network can be operated at room temperatures.              Using photons-means that they could also use the optical fibers that today's classical communication flows through.  But here's where problems start to appear.  Optical fibers are made of thin strands of glass, and glass has imperfections. When single photons, or pulses of light, travel down them, it can go smoothly for a bit, but over time and distance, the amplitude of the signal shrinks because the light scatters off impurities.  For the classical internet, the solution is repeaters. These are thumb-sized devices that are put at every 50 miles or so to amplify the signal and send it on.   The quantum world has tricky rules. Quantum bits (qubits), unlike classical bits, are not either a 0 or 1.  They're a superposition of the two, which means that they can be either 0, 1 or both at the same time.  You may see a qubit depicted as a sphere with an arrow emenating from its center.  You can't copy a quantum state and looking at it or observing it pulls it out of superposition, so you destroy the qubit. (The advantage of this is that it makes quantum links tamper-proof).