ght. The system really is in some sense in all the classical-like states at once! If the superposition can be protected from unwanted entanglement with its environment (known as decoherence), a quantum computer can output results dependent on details of all its classical-like states. This is quantum parallelism - parallelism on a serial machine. And if that wasn't enough, machines that would already, in architectural terms, qualify as parallel can benefit from quantum parallelism too - at which point the mind begins to seriously boggle! Why is Quantam Computing an exciting prospect: Quantum computation is an exciting prospect, because a quantum computer (if it could be built) would beexponentially faster than a classical computer on some problems. For example, a quantum computer couldfind prime factors in polynomial time instead of the exponential time required by a classical computer,thereby breaking conventional cryptographic codes. The problem with building a quantum computer is that the quantum bits (called qubits) simultaneouslyneed to be protected from the environment so that they retain their quantum phase, but they need to becoupled to the environment so that initial conditions can be loaded, the calculation applied, and the resultsread out. Because of these apparently contradictory constraints, it's taken a heroic experimental effort tomake just a 2 bit quantum computer. This has been done in systems such as trapped ions, or cavityquantum electrodynamics, that carefully isolate the qubits and cool them to their ground state. Neil Gershenfeld and Isaac Chuang have developed an entirely new approach to quantum computationthat promises to solve many of these problems. Instead of carefully isolating a small number of qubits, weuse a large thermal ensemble (such as a cup of coffee). Such a system has ~10^23 degrees of freedom;by applying RF pulses that excite nuclear magnetic resonances, we can create a tiny deviation fromequilibriu...
