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What are devices and their interconnections used alongwith Quantum Processors? Are they compatible with hardware devices like Cache, RAM, Disks of current computers?

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What you describe as current computers is known as the von Neumann architecture. This approach is one of many ways to think about classical computation and there are other classical approaches that might or might-not have relevant generalizations to quantum computing. The von Neumann architecture seems to be unlikely to be relevant to quantum computing, due to its difficulty from both the theoretical and implementation side.

However, as I mentioned on cstheory there is an article on implementing a quantum von Neumann architecture. They do this via superconducting qubits, of course the implementation is very small, with only 7 quantum parts: two superconducting qubits, a quantum bus, two quantum memories, and two zeroing registers. This allows their quantum CPU to perform one-, two-, and three-qubit gates on qubits, and the memory allows (data) qubits to be written, read out, and zeroed. Implementing a quantum superposition of gates is very difficult, and so the program is stored classically.

More likely models of quantum computing to be implemented include: measurement-based, topological, and adiabatic models. Typical implementations of these models look more like physics experiments (which they are!) than computers. Some of the common strategies for implementation include trapped ions, quantum optics, and superconducting circuits.

The circuit approach has been placed on chips and in fact D-Wave (a spin-off from UBC in Vancouver) claims to have built quantum-like computers using the adiabatic model to implement quantum simulated annealing. They have managed to sell this computer to Lockheed Martin but their approach has been met with heavy skepticism.

Lastly, the NMR approach mentioned by @RanG. is interesting, but suspected to be not equivalent to full quantum-computing. It is equivalent to the one-clean qubit model (also known as DQC1) and suspected to be strictly weaker than full quantum computing.

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  • $\begingroup$ So how and where do they store their information?. As in 'classical' computers store them as bits on silicon chips. $\endgroup$ – check123 May 8 '12 at 17:02
  • $\begingroup$ @check123 how does lambda calculus store its information? How does a neural network store its information? Both of those are also classical computers. You are thinking of a particular implementation (the von Neumann architecture). How information is stored is implementation dependent. A super-conducting qubit stores information in the quantum state of the handedness of the current, an optics experiments stores it in the polarization of the photon, or in the presence or absence of a photon, a super-cold ion experiment stores it in spin. $\endgroup$ – Artem Kaznatcheev May 8 '12 at 17:17
  • $\begingroup$ A topological implementation stores its information in the past history of paths of anyons, an adiobatic implementation stores the information throughout the whole hamiltonian. The point is that you can't ask "how does a quantum computer store information" no more than you can ask "how does any classical computer store information". You can only talk about specific implementations (you were conflating "classical computer" with "von Neumann architecture for classical computer"). Hope that helps :D $\endgroup$ – Artem Kaznatcheev May 8 '12 at 17:18
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Not really. Quantum-computers will need to be able to process quantum-bits (qubits) rather than "classical" bits.

Current devices (RAMs, disks) use nowdays technology to maintain classical bits: for instance, a memory cell (say, a capacitor) with high-voltage is "holding" the bit value "1"; if the voltage is low the bit is "0".

Qubits are "implemented" via very small "particles": photons, atoms, small molecules, and their "state" (energy level, etc.) is the "value". Those cannot be saved via a capacitor, for instance.

However, a quantum-computer will definitely have "classical" parts (like having two computers connected, one is classical and one quantum; if there is a computation to make, the classical part will be active; when a quantum effect is needed, the quantum part will be active). So quantum-computer will use standard RAMs, DISKs as well as other quantum-devices.

For the quantum-devices themselves: this depends much on the implementations. Optical devices will be used to manipulate photons. NMR computers will need to have a giant magnets, etc. (I'm not really familiar with implementation, but wikipedia seems to have several examples that you can start with).

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