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I would like to check something.

Consider I am working on cQED (superconducting qubits), or ion trapped, or silicon qubits (I would like to exclude "exotic for me" quantum computing like photon based, or topological Q.C).

The fastest you perform a gate, the less the noise has the time to act for noise "per unit time" acting (not all noise can be modelled this way but it can often be).

It is thus important to perform gate "the fastest possible".

My question is thus: What is limiting gate speed ?

About limitations I know: for superonducting qubit too short pulses are not a good solution as it might excite the system into higher than qubit level (making it leave the computational space). I would like to know what are the main limitations in general because I guess this is not the only one.

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  • $\begingroup$ what kind of architecture are you thinking of? $\endgroup$
    – glS ♦
    Mar 2, 2020 at 19:29
  • $\begingroup$ @glS you can focus on circuit QED for example. But I hope the answer to be "kinda" architecture independent (ie valid for different, but not all, architectures). It might be the case if my guess is correct. $\endgroup$
    – Marco Fellous-Asiani
    Mar 2, 2020 at 19:30

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There has been some early studies on the speed limits of speed limits for quantum gates in multi-qubit systems by S. Ashhab, P. C. de Groot, and Franco Nori published in Physical Review. As per this research, it is found that the three-qubit Toffoli gate time varies greatly depending on the type of interactions and the system's geometry, taking only slightly longer than a two-qubit controlled-not (CNOT) gate for a triangle geometry. As per this research, the fidelity of the CNOT and SWAP gates are plotted in the following diagrams.

The fidelity of the CNOT gate as a function of the allowed time (t) in the case of Ising interactions.

The fidelity of the CNOT gate as a function of the allowed time t

The fidelity of the √swap gate as a function of the allowed time (t) in the case of Heisenberg interactions.

The fidelity of the √swap gate for the pulse obtained as a function of the allowed time t

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