Feature Request: Any amount of control Qbits

[tjf801]

it would be nice to be able to add any amount of "control points" to any gate, and if you have time, an inverted "control point" would be nice also.

[perak]

@tjf801 thank you! Added to our list.

[perak]

@tjf801 by the way, I guess you already know that, but just in case to say that workaround is:

• you can make n-control-NOT with multiple toffoli gates (requires adding ancilla qubits)

  

• open circle (inverted control) can be done by surrounding control with X gates:

[perak]

Workaround until we implement it natively.

[tysonwolker]

Would love to see this natively, has there been any updates?

[perak]

You deserved it after 2 years of waiting! :) Added to dev pipeline.

[perak]

@tjf801 @tysonwolker

basic support for multi-controlled gates and inverted controls is now added to v0.9.186. Only u1 and x for now.

Usage:

Multi-controlled u1

var circuit = new QuantumCircuit();

// register controlled u1 gate with 3 controls
circuit.registerGate("mcu1_3", circuit.MCU1Circuit(3).save(true));

// And now you can add it anywhere into your circuit (with lamda of your choice)
circuit.appendGate("mcu1_3", [0, 1, 2, 3], { params: { lambda: "pi/3" } });
circuit.appendGate("mcu1_3", [2, 3, 0, 1], { params: { lambda: "pi/2" } });

console.log(circuit.exportQASM());

Output is:

OPENQASM 2.0;
include "qelib1.inc";
qreg q[4];
gate mcu1_3(lambda) a, b, c, d
{
  cu1 (lambda / 4) c, d;
  cx c, b;
  cu1 (-(lambda / 4)) b, d;
  cx c, b;
  cu1 (lambda / 4) b, d;
  cx b, a;
  cu1 (-(lambda / 4)) a, d;
  cx c, a;
  cu1 (lambda / 4) a, d;
  cx b, a;
  cu1 (-(lambda / 4)) a, d;
  cx c, a;
  cu1 (lambda / 4) a, d;
}

mcu1_3 (pi / 3) q[0], q[1], q[2], q[3];
mcu1_3 (pi / 2) q[2], q[3], q[0], q[1];

Multi-controlled x

var circuit = new QuantumCircuit();

// Register controlled x gate with 4 controls
circuit.registerGate("mcx_4", circuit.MCXCircuit(4).save(true));

// And use it in your circuit
circuit.appendGate("mcx_4", [0, 1, 2, 3, 4]);
circuit.appendGate("mcx_4", [2, 3, 0, 1, 4]);

console.log(circuit.exportQASM());

Output is:

OPENQASM 2.0;
include "qelib1.inc";
qreg q[5];
gate mcx_4 a, b, c, d, e
{
  h e;
  cu1 ((pi) / 8) d, e;
  cx d, c;
  cu1 (-((pi) / 8)) c, e;
  cx d, c;
  cu1 ((pi) / 8) c, e;
  cx c, b;
  cu1 (-((pi) / 8)) b, e;
  cx d, b;
  cu1 ((pi) / 8) b, e;
  cx c, b;
  cu1 (-((pi) / 8)) b, e;
  cx d, b;
  cu1 ((pi) / 8) b, e;
  cx b, a;
  cu1 (-((pi) / 8)) a, e;
  cx d, a;
  cu1 ((pi) / 8) a, e;
  cx c, a;
  cu1 (-((pi) / 8)) a, e;
  cx d, a;
  cu1 ((pi) / 8) a, e;
  cx b, a;
  cu1 (-((pi) / 8)) a, e;
  cx d, a;
  cu1 ((pi) / 8) a, e;
  cx c, a;
  cu1 (-((pi) / 8)) a, e;
  cx d, a;
  cu1 ((pi) / 8) a, e;
  h e;
}

mcx_4 q[0], q[1], q[2], q[3], q[4];
mcx_4 q[2], q[3], q[0], q[1], q[4];

Inverted controls

When creating gate, instead of simply providing number of control wires, you can provide array of boolean values where true is normal control and false is inverted.

Example: 3-controlled x gate with second control inverted:

var circuit = new QuantumCircuit();

// Register controlled x gate with 3 controls. Second control is inverted:
circuit.registerGate("mcx_3_101", circuit.MCXCircuit([true, false, true]).save(true));

// And use it in your circuit
circuit.appendGate("mcx_3_101", [0, 1, 2, 3]);
circuit.appendGate("mcx_3_101", [2, 3, 0, 1]);

console.log(circuit.exportQASM());

Output is:

OPENQASM 2.0;
include "qelib1.inc";
qreg q[4];
gate mcx_3_101 a, b, c, d
{
  x b;
  h d;
  cu1 ((pi) / 4) c, d;
  cx c, b;
  cu1 (-((pi) / 4)) b, d;
  cx c, b;
  cu1 ((pi) / 4) b, d;
  cx b, a;
  cu1 (-((pi) / 4)) a, d;
  cx c, a;
  cu1 ((pi) / 4) a, d;
  cx b, a;
  cu1 (-((pi) / 4)) a, d;
  cx c, a;
  cu1 ((pi) / 4) a, d;
  x b;
  h d;
}

mcx_3_101 q[0], q[1], q[2], q[3];
mcx_3_101 q[2], q[3], q[0], q[1];

Warning! Achtung! In moment of writing this: not tested well!

[perak]

Now this works in GUI as well: https://youtu.be/0ujizq7iat0