Many consider quantum computing the gateway to a new world of fast-thinking, intelligent computers. While classic computers process information as bits, quantum computing uses qubits. As a comparison, the classic bit is represented by a coin that can only show heads or tails, whereas qubits are more like a coin that spins as it is being tossed. In addition to the equal probability of ending up on either side, its other properties include spinning speed, the direction of the spin, the angle of the spinning axis, and so forth. All these properties may be used to carry data, but only for as long as the coin is spinning. As soon as it lands on the ground it will once again end up with one side up, and the exciting qubit turns into a boring old bit.1
Secure Data Transfer
While IBM, Google, and their respective research networks are working on augmenting quantum computing, others have set their eyes on another aspect of the quantum future of how it may affect cybersecurity and data encoding.
Quantum computing poses a potential threat in that it is capable of rapidly decoding existing encryption methods. One readily available solution is quantum key distribution (QKD). The first theoretical principles of quantum encryption were established as early as the 1980s. Most commonly, single photons are randomly put into distinct states of polarization that are transmitted from an information source (Alice) to a recipient (Bob), where they are retransferred into digital information.²
One of the most secure forms of establishing a trusted connection between Alice and Bob is the use of entanglement. There is a magical band between a pair of photons created as twins, causing one of them to behave exactly like the other, even if they are miles apart. Scientists call this “spooky action at a distance.” One entangled photon is transmitted to Bob, while the other returns to Alice, and both data and code information can be transmitted at the same time.
Long-Distance Communication Challenges
Using modern fiber technology, QKD may be applied today, but only on a metropolitan level. Due to the optical attenuation of fibers, the signals can only be transmitted for a few hundred kilometers before they are degraded into indistinguishable blabber. In legacy technologies, optical or electronic repeaters are used to overcome these obstacles, however, on a quantum level these technologies are not likely to be available within the next few decades. Unlike radio transmissions, the free-air transmission of optical data relies on the “line of sight,” which is the uninterrupted line between the sender and the recipient. Scientists are setting their minds beyond the confines of our planet. The attenuation of the atmosphere is far lower than that of an optical fiber. Effective communication is possible over significantly longer distances, given suitable sensitive single photon detectors. An entangled quantum code generated by a satellite in Earth’s orbit could be transferred to both Alice and Bob if they are both within reach of the satellite.
In 2017, the Micius satellite of the Chinese Academy of Science was successfully used to transfer a traditional quantum code from China to Vienna, Austria. At the National University of Singapore, scientists are currently working on an entangled quantum encryption device that will fit into a nano-satellite cube of 11.35 cm × 10 cm × 10 cm. The aptly named SpooQySat, in operation since June 17, 2019, currently serves as a live demonstration of an entangled photon source in space.
Meanwhile, here on earth, the detectors on Bob’s side must be able to filter out a single encoded photon from surrounding background noise. Scientists employ single photon avalanche diodes that absorb incoming photons and transfer them into electrical signals. Quality is defined by their quantum efficiency and the ability to block out background noise.
1https://www.sciencealert.com/quantum-computers
2https://en.wikipedia.org/wiki/Quantum_key_distribution
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Every Photon Counts
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