This perennial quest for a perfectly secure message spurred Seth Lloyd, a professor of quantum information at MIT, to put forth a theory of quantum enigma machines in 2013. This device, which derives its name from a Nazi-era cipher machine called Enigma, would use the quantum states of individual photons to encode and encrypt messages by altering properties of the photon wave, such as amplitude or wavelength. Unlike quantum key distribution, which uses principles of quantum mechanics to encrypt messages which are then sent over traditional communication channels like fiber optic cables or telephone lines, the quantum enigma machine would be capable of transmitting quantum states through a quantum channel between the sender and receiver. Moreover, the key used to encrypt this message is shorter than the message itself, an experimental method of encryption known as quantum data locking.
The idea for the device was intriguing, but due to technological limitations remained purely theoretical until last May, when a team of researchers managed to create a real quantum enigma machine in their lab for the first time.
The research team was led by Daniel Lum, a graduate student at the University of Rochester who hadn’t even heard of a quantum enigma machine until a little over a year ago, when he stumbled upon Lloyd’s arXiv paper describing the theoretical device. Intrigued, Lum brought up his discovery with the head of his lab, the physicist John Howell, at their next meeting and pitched it as a possible research project. Encouraged by his lab colleagues’ interest in the idea, Lum reached out to Lloyd and a handful of researchers at the National Institute of Standards and Technology who assisted him in designing an experiment that would put Lloyd’s quantum enigma theory to the test.
The quantum enigma machine ultimately created by Lum and his colleagues is elegantly simple in its design, but remarkably complex in its mechanics. At its most basic level the enigma machine consists of three core components: a device capable of generating single photons, two spatial light modulators, and an 8×8 array of nanowires.
