According to Wikipedia's timelines, quantum computing may have had some inceptions as early as the late 60's, when Stephen Wiesner invented conjugate coding.
Around the early 80's, Wiesner's ideas inspired Charles Bennett and Gilles Brassard to hypothesize a cryptographic scheme - now called BB84 - to use quantum mechanics to enable information-theoretically secure cryptographic communication.
I sense that in the mid 80's, quantum key distribution was at best somewhat well-received, but more likely mostly ignored. Nonetheless researchers really began to take notice and appreciation when Bennett, et al. built a working prototype machine that transmitted and received a plurality of qubits, encoded in the polarity of photons, over a short distance to implement the BB84 scheme:
I recall seeing the prototype in my copy of Scientific American in 1992. From Brassard's remembrances:
Essentially without any special budget allocated to the project, we were able, in late October 1989, to establish history’s first secret quantum transmission, over a staggering distance of 32.5 centimetres...!
Clearly this prototype wasn't practical or useful, but I'd posit that the theoretical and experimental researchers in the then nascent field of quantum computing/quantum information science were inspired not just by the theoretical work on BB84 but by images and descriptions of the above actual, physical tabletop device, as bulky and noisy as it was.
Based on the SciAm article the device was built at IBM Yorktown Heights (where Bennett had worked since '74).
As to my question, could the prototype still exist anywhere? Or put in a basement in IBM's campus and forgotten about, or was it more than likely scavenged for parts?
Such a prototype might be worth saving, at the very least as a bit of a relic to the field of quantum information...
The SciAm article was in '92. Around then, Vazirani gave a famous lecture at Bell Labs on the Bernstein-Vazirani algorithm, with Shor (and maybe Simon?) in the audience. We also have the quantum teleportation protocol from '93, the Elitzur-Vaidman bomb tester from then as well...