The origins of quantum physics date back more than 100 years - with the recognition that energy consists of discrete packets called quanta. Albert Einstein’s explanation of the photoelectric effect - showing that light itself is composed of quanta that we now call photons - was among the seminal discoveries triggering a quantum revolution in physics.
By the 1930s, most of the mind-boggling theories of quantum physics had been fully articulated. Individual photons of light appear to pass simultaneously through multiple slits in the famous twin slit experiment, providing they are not observed. The photons are superimposed across multiple states. Attempts to measure the path of the photons causes them to collapse into a single state. Heisenberg’s uncertainty principle formalizes the notion that you cannot observe quantum state without altering it.
Conventional View of Quantum Physics Examplified by 'Schrödinger's Cat'
As Niels Bohr famously said, “If quantum mechanics hasn't profoundly shocked you, you haven't understood it yet.” The conventional view of quantum physics is that multiple simultaneous probabilities do not resolve until they’re perceived by a conscious observer. This Copenhagen interpretation serves as the basis for the famous Schrödinger's cat thought experiment, in which a cat is simultaneously dead and alive when unobserved in an elaborate quantum contraption. (Some have conjectured that Schrödinger's dog actually proposed this experiment.)
The competing explanations for quantum phenomenon have powered many a science fiction story. The many worlds interpretation of quantum physics asserts that every quantum decision point is realized in alternative realities that result in a myriad of alternative universes, many of which vary from our own in only subtle ways.
The undeniably mind-boggling weirdness of various quantum interpretations does not limit the impact of quantum mechanics on modern technology. Quantum physics has been an extraordinarily successful theory in explaining the universe, especially in the realm of the very small. However, quantum theory soon stands to have an even more revolutionary effect through the introduction of quantum computers and quantum encryption.
Quantum Computing Raises New Possibilities
Quantum computing was popularized by physicist Richard Feynman in the 1980s. The essential concept is to use subatomic particle behavior as the building blocks of computing. In essence, the logic gates and silicon-based building blocks of today’s physical computers would be replaced by interactions between subatomic particles.
As well as providing a mechanism for leapfrogging the limitations of silicon-based technology, Quantum computing also raises the possibility of completely revolutionizing cryptography. Quantum computers may use quantum bits (qubits) rather than traditional bits to store information. Information in a qubit can be a superimposed version of all possible states. A qubit-powered computer could rapidly determine prime factors for large numbers - which could render today’s public/private key encryption schemes obsolete. It’s hard to imagine a more significant technological disruption than the elimination of current encryption schemes.
Another quantum effect provides the ability to increase the security of communication. Quantum key distribution provides a mechanism of securing a channel for the transmission of an encryption key. By leveraging the Heisenberg uncertainty principle, the encryption keys are sent over a quantum channel. Any attempt by a third party to read the key effectively destroys the key or allows the eavesdropping to be detected. Unfortunately, the effect cannot survive router hops, so it’s currently limited to line-of-sight dedicated optical fibre with a maximum range of a few hundred kilometers
Quantum techniques also are being used to improve the randomness of computer-based random number generators. While this may sound trivial, random numbers are frequently used to “seed” encryption keys and failures of randomness have led to many security exploits.
The development of a functional and practical quantum computing system has been “pending” for some decades now, but there are some real signs that this technology may become decisive soon. The implications of cryptography are encouraging major government investment - both the U.S. and China, in particular, are heavily investing in quantum computing technology. The arms race to develop functional quantum computing has begun.