Support multi moment gauge compiling

[babacry]

Support multi moment gauge transformation, where target moments will be gauged with new moments, e.g.,

        q₀: ... ───LG0───╭───────────╮────RG0───...
                         │           │
        q₁: ... ───LG1───┤  moments  ├────RG1───...
                         │   to be   │
        q₂: ... ───LG2───┤ gauged on ├────RG2───...
                         │           │
        q₃: ... ───LG3───╰───────────╯────RG3───...

• A common MultiMomentGaugeTransformer class is defined.
• Implemented the CPhase multi moment gauge CPhaseGaugeTransformerMM.
• A moment is a target moment if it contains at least one target op (CZPowGate) and all its operations are supported by this transformer.
• A couple of single qubit gates are supported for CPhaseGaugeTransformerMM, e.g., Pauli Gates, ZPowGate etc. If these gates are detected, gauge will be calculated accordingly. Users can tweak their desired gates by instantiate their own transformer by transformer = CPhaseGaugeTransformerMM(supported_gates=ops.Gateset(g1,g2,g3)). By default _SUPPORTED_GATESET are used.

Example:

  Input:
                  ┌──┐
    0: ───@────────@─────H───Rz(-0.255π)───────────@───────@───────
          │        │                               │       │
    1: ───@^0.2────┼@──────────────────────────────@^0.1───@───────
                   ││
    2: ───@────────@┼────────@─────────────@───────@───────@───────
          │         │        │             │       │       │
    3: ───@─────────@────────@^0.2─────────@^0.2───@───────@^0.2───
                  └──┘
    Output:
                       ┌──┐
    0: ───Y───@─────────@─────PhXZ(a=0,x=1,z=0)───H───X───Rz(0.255π)────────────@───────@────────PhXZ(a=0,x=1,z=1.1)───
              │         │                                                       │       │
    1: ───I───@^-0.2────┼@────Z^0.2───────────────────Y─────────────────────────@^0.1───@────────PhXZ(a=0,x=1,z=0.1)───
                        ││
    2: ───X───@─────────@┼────PhXZ(a=0,x=1,z=1)───────X───@────────────@────────@───────@────────PhXZ(a=0,x=1,z=0)─────
              │          │                                │            │        │       │
    3: ───Z───@──────────@────I───────────────────────I───@^-0.2───────@^-0.2───@───────@^-0.2───Z^-0.4────────────────
                       └──┘

Usage

case 1: default setup, any moment with CZPowGate and optionally with _SUPPORTED_GATES will be gauged (see example above),

cphase_transformer = CPhaseGaugeTransformerMM()
output_circuit = cphase_transformer(input_circuit)

case 2: Only CZPowGate-only moments will be gauged (see test_gauge_on_czpow_only_moments test case),

cphase_transformer = CPhaseGaugeTransformerMM(supported_gates=cirq.Gateset())
output_circuit = cphase_transformer(input_circuit)

[codecov]

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[babacry]

Hey @eliottrosenberg @NoureldinYosri , here is multi moment gauge compiling!! After evaluating multiple strategies, this approach proves to be optimal regarding both execution speed and future extensibility.

Note gauges could be automatically added to circuits with default setup, wonder if the default setup is suitable for most use cases? (see Example section and Usage section in the description above)

[eliottrosenberg]

LGTM! Great work, @babacry!

[NoureldinYosri]

@babacry is there a way to reuse code you wrote before in _PauliAndZPow ?

[NoureldinYosri]

didn't you implement the logic for pulling gates somewhere else? or is this specific to these gates?

[babacry]

Not really, existing functions only allow for pulling Pauli gates through Clifford gates. However, the cphase gate is non-Clifford. When a Pauli operator is pushed through a cphase gate, it transforms into a combination of a Pauli operator and a Z-rotation. To handle this, the method tracks both the Pauli operator and the additional Z-rotation throughout the moments.

[babacry]

Thanks Nour for the insightful reivews!

We don't have a _PauliAndZPow support in cirq yet. If you are mentioning the PR I worked on to support a specific use case of multi moment gauge compiling, the pr is closed. The only pull-through support in cirq is pulling Pauli gates through Cliffords.

Could you help take another look? I've resolved some comments by committing changes, also left some comments for further discussions for the use of @attrs.frozen. @NoureldinYosri

[NoureldinYosri]

initial review of style ... I still haven't reviewed the logic of commuting gates

[babacry]

Thanks for the careful and insightful reviews, @NoureldinYosri !

I've frozen attributes in classes instead of allowing inplace updates. And a couple of other comments are addressed. Please help take another look, thanks!