I have been interested in the idea of computer clusting which is about making multiple pysical computer system to act as one whole logical computer system computing the same task at the same time, but what about this idea in the quantum computing world has it been done or proposed before?
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2 Answers
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Yes, this has been thought about. For example, the plan for scaling up ion trap computers involves having multiple "modules", each with a few dozen qubits. When qubits in separate modules need to interact, they are moved to the same module using quantum teleportation or some other quantum channel. Each "module" is like a little quantum computer in a cluster, with the cluster forming a larger quantum computer.
Example paper: Co-designing a scalable quantum computer with trapped atomic ions
answered Oct 15, 2018 at 4:47
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1$\begingroup$ One module may need better coherence and can sacrifice on operations performed and another may not be able to make the same sort of sacrifices. Each module has their role. $\endgroup$– AHusainCommented Oct 15, 2018 at 4:59
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The concept of quantum computing clusters could be formalised into a generalised distributed quantum computers. We will need both quantum networks and distributed quantum computing algorithms to realise such distributed quantum computers. These distributed quantum computers work by linking multiple quantum processors through a quantum network by sending qubits in-between them. Doing this creates a quantum computing cluster and therefore creates more computing potential.
It is already proven that even in case of small quantum devices, two clustered devices can provide an exponential speedup with respect to isolated devices. As mentioned in the other answer, quantum teleportation is the key strategy to enable distributed quantum computing, which requires to perform operations between qubits physically located on multiple remote quantum devices. However there is a trade off to this teleportation operation. There will be a time overhead induced by teleporting operations in distributed quantum computing.
Currently quantum processors are only separated by short distances. To scale this quantum networks, we will need better quantum communication links and secure quantum key distribution systems. To make such an infrastructure, we will need optical switches capable of delivering qubits to the quantum processors. These switches need to preserve the quantum coherence. We will also need quantum repeaters to transport qubits over long distances. Since qubits cannot be copied, classical signal amplification would not be possible.
