Quantum Computing Almost Here

R. Colin Johnson 
IBM recently demonstrated the components necessary to build a quantum computer, including superconducting microchips that can be mass produced in conventional semiconductor fabrication facilities.IBM has demonstrated the key components for a quantum computer capable of supercomputer-caliber performance on the desktop, near instantaneous search-and-sorts of Big Data, and uncrackable encryption. The three components included a superconducting quantum memory, a mass-producible quantum chip, and a universal quantum logic-gate. Next IBM aims to reap a hundred-fold performance improvement by optimally combining these pieces into a complete quantum computer. "We only need another factor or 10 to 100 improvement to build a complete quantum computer," said Matthias Steffen, IBM's manager of Experimental Quantum Computing. "But to put that in perspective, we needed a factor of 10,000 improvement back when quantum computers were first proposed in 1999--now we are getting very close." Quantum computers gain their almost magical capabilities by using q-bits, instead of binary bits, that represent superpositions of all binary values simultaneously. For instance, a two q-bits can represent all four binary values--(0,0), (0,1), (1,0) and (1,1)--simultaneously. Thus performing a two q-bit multiplication will simultaneously perform the operation on all four values at once. Likewise, an eight q-bit value can represent all 256 binary values at once, a quantity that doubles again for each added q-bit. Theoretically, thousands of simultaneous operations can be performed by long strings of q-bits, which is exactly why they hold so much computational promise. In fact, IBM estimates that a single 256 q-bit value contains more binary bits of information that there are particles in the universe. The main stumbling block overcome by IBM was the amount of time in which a q-bit can be held in the superposition state. All sorts of external environmental influences--from stray electric fields to thermal emissions--can cause a q-bit to "relax" from a superposition of simultaneous binary values into a single one. In fact, this is desirable at the end of each quantum computation, since just such a relaxation is performed to choose the optimal result from among those that were simultaneously computed. However, in the past these so-called "coherence" times were measured in microseconds, which is not long enough for the kind of error-correction needed to detect inadvertent errors during a quantum calculation and correct it on-the-fly. Most of the error correction schemes proposed today require coherence times in excess of .1 millisecond, making IBM's demonstration today a milestone. The next steps for IBM are the tough engineering optimizations needed to enable superconducting quantum computers to communicate using ultra-high-frequency microwave electronics.