Multicontrol Rz fix #9574

AlexisRalli · 2023-02-13T16:09:08Z

Summary

I've currently written code to decompose multi control rotation gates properly (see issue 9202 ): QuantumCircuit.mcrz, QuantumCircuit.mcrx, QuantumCircuit.mcry

The update includes a new file in generalized_gates that for any given single qubit unitary matrix will generate a multicontrol quantum circuit of it using O(n^2) two qubit gates.

Details and comments

Currently there are problems with the unit tests. I think this could stem from the following:

from qiskit import QuantumCircuit, transpile
import numpy as np

angle = -np.pi/3
tt = QuantumCircuit(1)
tt.rz(angle, 0)

gg = tt.to_gate()

gg = gg.control(1, 'TEST', '1')

bb =  QuantumCircuit(2)
bb.append(gg, [0,1])



print(bb.decompose().decompose().draw())

>> 
                                      ┌────────────┐
q_0: ──────────────■───────────────■──┤ U(0,0,π/6) ├
     ┌──────────┐┌─┴─┐┌─────────┐┌─┴─┐└────────────┘
q_1: ┤ Rz(-π/6) ├┤ X ├┤ Rz(π/6) ├┤ X ├──────────────
     └──────────┘└───┘└─────────┘└───┘

i.e. there is a relative phase in the gate decomposition that should NOT be there. I think the unit tests take this into account, when they should not. However, by correcting the codebase these tests then fail.

Note the updated code for QuantumCircuit.mcrz builds the correct quantum circuits:

angle = -np.pi/3
vv = QuantumCircuit(2)
vv.mcrz(angle, [0],1)
print(vv.decompose().draw())

                                      
q_0: ──────────────■───────────────■──
     ┌──────────┐┌─┴─┐┌─────────┐┌─┴─┐
q_1: ┤ Rz(-π/6) ├┤ X ├┤ Rz(π/6) ├┤ X ├
     └──────────┘└───┘└─────────┘└───┘

How should I proceed?

Thanks for the help!

(side note) The MCU2Gate class allows arbitrary control single qubit gates to be built as follows:

from qiskit import QuantumCircuit
from scipy.stats import unitary_group
from qiskit.circuit.library.generalized_gates.multicontrol_arb_gate import MCU2Gate

ctrl_state = '110'
n_c = len(ctrl_state)
U = unitary_group.rvs(2) # random unitary

test_gate = MCU2Gate(U,
                n_c,
                ctrl_state)

nq = test_gate.num_qubits
IBM_c = QuantumCircuit(nq)
IBM_c.append(test_gate, range(nq))
IBM_c.draw()
>>
q_0: ───■────
        │    
q_1: ───■────
        │    
q_2: ───o────
     ┌──┴───┐
q_3: ┤ U(2) ├
     └──────┘

…e functionality added

qiskit-bot · 2023-02-13T16:09:12Z

Thank you for opening a new pull request.

Before your PR can be merged it will first need to pass continuous integration tests and be reviewed. Sometimes the review process can be slow, so please be patient.

While you're waiting, please feel free to review other open PRs. While only a subset of people are authorized to approve pull requests for merging, everyone is encouraged to review open pull requests. Doing reviews helps reduce the burden on the core team and helps make the project's code better for everyone.

One or more of the the following people are requested to review this:

@Cryoris
@Qiskit/terra-core
@ajavadia

CLAassistant · 2023-02-13T16:09:13Z

All committers have signed the CLA.

AlexisRalli · 2023-02-13T16:12:54Z

@javabster @jakelishman @1ucian0 - Thanks for your help during the qiskit office hours. It turns out the code still fails some unit tests even without the mcx functionality.

jakelishman · 2023-02-13T16:14:00Z

@alexanderivrii, @Cryoris (and @ShellyGarion, I think?): please could you two (three if I'm right about Shelly too) have a look at this? Alexis came to the office hours earlier today and we talked about what he'd been working on, and in principle it all looks like something we're very interested in to me.

Sasha: for you, my questions are mostly about how you think it's best to organise the code in the short-term with other synthesis efforts going on. I suspect that it's mostly ok to mirror the current style, since our hope is to more completely overhaul MCX/MCU/etc synthesis later.

Julien and Shelly: I think Julien you did the original (or most recent) implementations of the MC synthesis routines, and Shelly you're definitely more up-to-date on the literature and other methods than I am.

AlexisRalli · 2023-02-13T16:19:55Z

@alexanderivrii, @Cryoris (and @ShellyGarion, I think?): please could you two have a look at this? Alexis came to the office hours earlier today and we talked about what he'd been working on, and in principle it all looks like something we're very interested in to me.

Sasha: for you, my questions are mostly about how you think it's best to organise the code in the short-term with other synthesis efforts going on. I suspect that it's mostly ok to mirror the current style, since our hope is to more completely overhaul MCX/MCU/etc synthesis later.

Julien and Shelly: I think Julien you did the original (or most recent) implementations of the MC synthesis routines, and Shelly you're definitely more up-to-date on the literature and other methods than I am.

Thanks @jakelishman - to reproduce the McX code run the following:

from qiskit.circuit.library.generalized_gates.multicontrol_arb_gate import MCU2Gate
from qiskit.quantum_info import Operator
from qiskit import QuantumCircuit, transpile
import numpy as np
from qiskit import QuantumCircuit

X = np.array([[0,1],[1,0]])

for n_controls in range(2,10): # < -- change range for more controls!
    cqbits = list(range(n_controls))
    targ = cqbits[-1]+1
    nc = max(*cqbits, targ)+1
    
    ###
    diag_circuit = QuantumCircuit(nc)
    diag_circuit.h(targ) # change from Z to X basis
    diag = np.ones(2**nc)
    diag[-1]=-1
    diag_circuit.diagonal(diag.tolist(), [*cqbits, targ])
    diag_circuit.h(targ) # change from Z to X basis
    diag_circuit = transpile(diag_circuit, basis_gates=['cx','u'])
    
    ###
    custom_mcX = QuantumCircuit(nc)
    custom_mcX_gate = MCU2Gate(X,
                        n_controls,
                       label='X')
    custom_mcX.append(custom_mcX_gate, [*cqbits, targ])
    custom_mcX = transpile(custom_mcX, basis_gates=['cx','u'])
    ##
    std_mcX = QuantumCircuit(nc)
    std_mcX.mcx(cqbits, targ, mode='noancilla')
    std_mcX = transpile(std_mcX, basis_gates=['cx','u'])
    
    assert(np.allclose(Operator(std_mcX).data,
                       Operator(diag_circuit).data))
    assert(np.allclose(Operator(std_mcX).data,
                   Operator(diag_circuit).data))
    ####
    print('N_controls:', n_controls)
    print('*'*10)
    print('DIAG :', diag_circuit.num_nonlocal_gates())
    print('NEW  :', custom_mcX.num_nonlocal_gates())
    print('OLD  :', std_mcX.num_nonlocal_gates())
    print()

This outputs the following (counts number of CNOT gates):

N_controls: 2
**********
DIAG : 6
NEW  : 10
OLD  : 6

N_controls: 3
**********
DIAG : 14
NEW  : 26
OLD  : 14

N_controls: 4
**********
DIAG : 30
NEW  : 50
OLD  : 36

N_controls: 5
**********
DIAG : 62
NEW  : 82
OLD  : 92

N_controls: 6
**********
DIAG : 126
NEW  : 122
OLD  : 188

N_controls: 7
**********
DIAG : 254
NEW  : 170
OLD  : 380

N_controls: 8
**********
DIAG : 510
NEW  : 226
OLD  : 764

N_controls: 9
**********
DIAG : 1022
NEW  : 290
OLD  : 1532

i.e. the diagonal approach should be used up to 5 controls and then the new decomposition after 6 controls

adjs · 2023-03-17T01:09:58Z

qiskit/circuit/library/standard_gates/multi_control_rotation_gates.py



 QuantumCircuit.mcrx = mcrx
 QuantumCircuit.mcry = mcry
 QuantumCircuit.mcrz = mcrz
+
+
+class ControlRotationGate(ControlledGate):


Hi @AlexisRalli, I think that ucry, ucrx and ucrz in this folder already implements Theorem 8 of https://arxiv.org/pdf/quant-ph/0406176.pdf.

adjs · 2023-03-17T01:14:17Z

qiskit/circuit/library/standard_gates/multi_control_rotation_gates.py

-    if n_c == 1:  # cu
-        _apply_cu(self, 0, 0, lam, control_qubits[0], target_qubit, use_basis_gates=use_basis_gates)
+    if n_c <= 6:
+        ncrz = ControlRotationGate(lam, n_c, axis="z")


You can probably use 'QuantumCircuit.ucrz' with several id gates and one rz. Or maybe adapt ControlRotationGate to use ucrz. Nice observation that with a small number of qubits the multiplexer is a good approach.

I think that mcrz should be in another PR, because the mcrz issue.

adjs · 2023-03-17T01:17:13Z

qiskit/circuit/library/standard_gates/multi_control_rotation_gates.py

-            use_basis_gates=use_basis_gates,
-        )
+    if n_c <= 6:
+        ncrx = ControlRotationGate(theta, n_c, axis="x")


Is it possible to use ucrx here?

adjs · 2023-03-17T01:17:50Z

qiskit/circuit/library/standard_gates/multi_control_rotation_gates.py

+        rygate = (
+            numpy.cos(theta / 2) * numpy.eye(2) - 1j * numpy.sin(theta / 2) * YGate().__array__()
+        )
+        ncry = MCU2Gate(rygate, n_c, label=f"Ry({theta:0.3f})")


Is it possible to use ucry here?

adjs · 2023-03-17T01:21:22Z

qiskit/circuit/library/generalized_gates/multicontrol_arb_gate.py

+from qiskit.extensions.quantum_initializer.squ import SingleQubitUnitary
+
+
+class MCU2Gate(ControlledGate):


My suggestion is to create a different PR with the MCU2Gate because this class is for "any multicontrol version of any single qubit unitary matrix (gate)" and this PR is about multicontrolled rotation gates.

adjs · 2023-03-17T01:25:42Z

Hi @AlexisRalli. I'm not on the qiskit team, but I left some suggestions. The main one is that this PR could be separeted in two. One for the MCU2Gate class and another for multicontrolled rotations with few control bits.

ShellyGarion · 2023-05-25T05:27:02Z

can we close this PR as #9836 has been merged?

1ucian0 · 2023-05-25T08:30:42Z

thanks @adjs for the review and #9836 !

@AlexisRalli, if you think #9202 is still not fixed or that #9836 is somehow incomplete, please open a new issue. If this PR has elements that are not covered by #9836, you can also open a new PR from a branch of AlexisRalli:multicontrol_rot_only_fix.

thanks!

AlexisRalli added 2 commits February 13, 2023 13:55

multicontrl rotation gate fixes and arb multicontrol single qubit gat…

54537db

…e functionality added

pylint and black run

2bd80e2

AlexisRalli requested a review from a team as a code owner February 13, 2023 16:09

qiskit-bot added the Community PR PRs from contributors that are not 'members' of the Qiskit repo label Feb 13, 2023

jakelishman mentioned this pull request Feb 16, 2023

Decompose CnXGate grows exponentially in terms of CX, instead of linear #5872

Closed

ShellyGarion mentioned this pull request Mar 2, 2023

[WIP] restructuring MCX synthesis code #7505

Closed

AlexisRalli added 3 commits March 6, 2023 13:45

updated to use ControlledGate class

7aa0f21

updated controls MC rotation gate controls

f71ee03

black and linting run

bcaae8f

ewinston self-assigned this Mar 8, 2023

AlexisRalli mentioned this pull request Mar 15, 2023

Fixes issue #9741 from exponential to linear number of cx gates in mcry #9688

Merged

adjs reviewed Mar 17, 2023

View reviewed changes

1ucian0 closed this May 25, 2023

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Multicontrol Rz fix #9574

Multicontrol Rz fix #9574

AlexisRalli commented Feb 13, 2023 •

edited

Loading

qiskit-bot commented Feb 13, 2023

CLAassistant commented Feb 13, 2023 •

edited

Loading

AlexisRalli commented Feb 13, 2023

jakelishman commented Feb 13, 2023 •

edited

Loading

AlexisRalli commented Feb 13, 2023 •

edited

Loading

adjs Mar 17, 2023

adjs Mar 17, 2023

adjs Mar 17, 2023

adjs Mar 17, 2023

adjs Mar 17, 2023

adjs Mar 17, 2023

adjs commented Mar 17, 2023

ShellyGarion commented May 25, 2023

1ucian0 commented May 25, 2023

		from qiskit.extensions.quantum_initializer.squ import SingleQubitUnitary


		class MCU2Gate(ControlledGate):

Multicontrol Rz fix #9574

Multicontrol Rz fix #9574

Conversation

AlexisRalli commented Feb 13, 2023 • edited Loading

Summary

Details and comments

qiskit-bot commented Feb 13, 2023

CLAassistant commented Feb 13, 2023 • edited Loading

AlexisRalli commented Feb 13, 2023

jakelishman commented Feb 13, 2023 • edited Loading

AlexisRalli commented Feb 13, 2023 • edited Loading

adjs Mar 17, 2023

Choose a reason for hiding this comment

adjs Mar 17, 2023

Choose a reason for hiding this comment

adjs Mar 17, 2023

Choose a reason for hiding this comment

adjs Mar 17, 2023

Choose a reason for hiding this comment

adjs Mar 17, 2023

Choose a reason for hiding this comment

adjs Mar 17, 2023

Choose a reason for hiding this comment

adjs commented Mar 17, 2023

ShellyGarion commented May 25, 2023

1ucian0 commented May 25, 2023

AlexisRalli commented Feb 13, 2023 •

edited

Loading

CLAassistant commented Feb 13, 2023 •

edited

Loading

jakelishman commented Feb 13, 2023 •

edited

Loading

AlexisRalli commented Feb 13, 2023 •

edited

Loading