Representation of Gates/Pulses

[pbethke]

Gates are logical operations on a single or multiple qubits. Their associated control signals are called pulses. The two concepts are strongly connected. Gates and pulses have the following properties:

Gates

• Gates are unitary operations performed on one or multiple qubits
• Gates can be concatenated to produce new gates
• Qubits usually have a set of gates that they can perform, forming a complete basis from which to compose any gate.
• The gates in a physical qubit's basis gate set each have an associated pulse

Pulses

• Pulses represent the actual control signal on the qubit
• Pulses map onto commands for the physical qubit control electronics

Problem

pulse and gate definitions somewhat overlap. We should find one term for it and stick to it. The way I try to separate the two is to always use gate down to the physical qubit level, where pulse becomes appropriate. Gates are then logical operations on qubits and may be static, whereas pulses depend on the qubit it is acting on, calibration, etc.

Qubit Hierarchy and Gates/Pulses

The top level corresponds to algorithms, the middle one to things like simulated versions of physical qubits or logical qubits and the bottom level is the level of real physical qubits, calibration and pulses.

[hbluhm]

It seems worth discussing if gates/algorithms (which also include other operations) and pulses/waveforms should be combined into one type of object or hierarchy or be separate entities representing the mathematical model on the one hand and control pulse on the other.

Also, I would suggest to only introduce different classes for different hierarchy levels if a natural, sharp distinction exists. (I am currently not aware of one.) Otherwise, operations and waveforms could be generic designations.

[pbethke]

the only real distinction here is that the gates that comprise the gate set of a physical qubit should map onto corresponding pulses and are not mere mathematical objects. One could argue of course, that a control signal itself is also a gate, but its form depends on calibration of the actual qubit, so its not as static as other gates.