Molecular computing uses single atoms or molecules to solve computational problems, including DNA computing, quantum computing, and nanoscale logic gates. A kilogram of carbon with 100 atoms could process over 1027 operations per second, replacing traditional silicon computers. DNA computing is powerful but not universal, while quantum computing faces challenges with decoherence. Nanoscale robotics are needed to manufacture an advanced molecular computer.
Molecular computing is a generic term for any computational scheme that uses single atoms or molecules as a means of solving computational problems. Molecular computing is most frequently associated with DNA computing, because it has made the most advances, but it can also refer to quantum computing or molecular logic gates. All forms of molecular computing are currently in their infancy, but in the long run they are likely to replace traditional silicon computers, which face barriers to higher levels of performance.
A single kilogram of carbon contains 5 x 1025 atoms. Imagine if we could only use 100 atoms to store a single bit or perform a computational operation. Using massive parallelism, a molecular computation weighing just a kilogram could process more than 1027 operations per second, over a billion times faster than today’s best supercomputer, which operates at about 1017 operations per second. With such a large computing power, we could achieve calculation and simulation feats that are unimaginable for us today.
Different proposals for molecular computers vary in the principles of their operation. In calculating DNA, DNA acts as the software while enzymes act as the hardware. The custom synthesized DNA strands are combined with enzymes in a test tube and, depending on the length of the resulting trailing strand, a solution can be derived. DNA computation is extremely powerful in its potential, but suffers from serious drawbacks. DNA computation is not universal, which means that there are problems it cannot, even in principle, solve. It can only return yes or no answers to computational problems. In 2002, researchers in Israel created a DNA computer capable of performing 330 trillion operations per second, more than 100,000 times faster than the fastest PC of the time.
Another proposal for molecular computing is quantum computing. Quantum computing takes advantage of quantum effects to perform the calculation, and the details are complicated. Quantum computing depends on supercooled atoms locked in entangled states with each other. One major challenge is that as the number of computational elements (qubits) increases, it becomes progressively more difficult to isolate the quantum computer from external matter, causing it to decoher, eliminate quantum effects and restore the computer to its classical state. This ruins the calculation. Quantum computing can still be developed into practical applications, but many physicists and computer scientists remain skeptical.
An even more advanced molecular computer would involve nanoscale logic gates or nanoelectronic components that conduct processing in a more conventional, universal and controlled way. Unfortunately, we do not currently have the manufacturing capacity to manufacture such a computer. Making this kind of molecular computer would require nanoscale robotics that can place each atom into the desired configuration. Preliminary efforts are underway to develop this type of robotics, but a major breakthrough could take decades.
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