ConjugationEnvironment error

[diehoq]

The following code raises Exception: Tried to perform operation cswap on unallocated qubit qbl_392.0, which seems to be a bug

def to_be_debugged(x, p, m):
    n = p.bit_length()
    u = qrisp.QuantumFloat(n)
    u[:] = p
    v = qrisp.QuantumFloat(n)
    v[:] = x
    r = qrisp.QuantumModulus(2 * p)
    r[:] = 0
    s = qrisp.QuantumModulus(2 * p)
    s[:] = 1

    f = qrisp.QuantumBool()
    f[:] = True
    for i in range(2 * n):
        a = qrisp.QuantumBool()

        with qrisp.control(a):
            qrisp.swap(u, v)
            qrisp.swap(r, s)
        # uncompute a
        qrisp.mcx([s[0]], a, ctrl_state="0")
        a.delete()

    r = p - r
    res = qrisp.QuantumModulus(p)
    for i in range(res.size):
        qrisp.swap(res[i], r[i])

    # Uncompute u,v,s,f
    f.flip()
    f.delete()
    qrisp.x(u)
    u.delete()
    v.delete()
    r.delete()
    s -= p
    s.delete()
    return res

p=7
t1 = qrisp.QuantumModulus(p)
t1[:] = 6
t2 = qrisp.QuantumModulus(p)
t2[:] = 2
m = qrisp.QuantumArray(qtype=qrisp.QuantumBool(), shape=(2*p.bit_length(),))
with qrisp.conjugate(to_be_debugged)(t1,p,m) as q:
    s = q*t2
for a in m:
    a.delete(verify=True)

ERROR:

{--------------------------------------------------------------------------- Exception Traceback (most recent call last) Cell In[29], [line 7](vscode-notebook-cell:?execution_count=29&line=7) [5](vscode-notebook-cell:?execution_count=29&line=5) t2[:] = 2 [6](vscode-notebook-cell:?execution_count=29&line=6) m = qrisp.QuantumArray(qtype=qrisp.QuantumBool(), shape=(2*p.bit_length(),)) ----> [7](vscode-notebook-cell:?execution_count=29&line=7) with qrisp.conjugate(to_be_debugged)(t1,p,m) as q: [8](vscode-notebook-cell:?execution_count=29&line=8) s = q*t2 [9](vscode-notebook-cell:?execution_count=29&line=9) for a in m:

File ~\Documents\GitHub\Qrisp\src\qrisp\environments\conjugation_environment.py:163, in ConjugationEnvironment.enter(self)
161 instr = temp_data.pop(i)
162 if isinstance(instr, QuantumEnvironment):
--> 163 instr.compile()
164 else:
165 self.env_qs.data.append(instr)

File ~\Documents\GitHub\Qrisp\src\qrisp\environments\control_environment.py:336, in ControlEnvironment.compile(self)
332 instruction.qubits = [self.condition_truth_value] + list(
333 instruction.qubits
334 )
335 # Append instruction
--> 336 self.env_qs.append(instruction)
338 perm_unlock(ctrl_qubits)
340 if inversion_tracker == -1:

File ~\Documents\GitHub\Qrisp\src\qrisp\core\quantum_session.py:446, in QuantumSession.append(self, operation_or_instruction, qubits, clbits)
444 if issubclass(operation_or_instruction.class, Instruction):
445 instruction = operation_or_instruction
--> 446 self.append(instruction.op, instruction.qubits, instruction.clbits)
447 return
450 elif issubclass(operation_or_instruction.class, Operation):

File ~\Documents\GitHub\Qrisp\src\qrisp\core\quantum_session.py:496, in QuantumSession.append(self, operation_or_instruction, qubits, clbits)
490 raise Exception(
491 f"Tried to perform operation {operation.name} on "
492 f"unallocated qubit {input}"
493 )
495 if operation.name not in ["qb_alloc", "barrier"]:
--> 496 check_alloc(qubits)
499 # We now need to merge the sessions and treat their differing environment
500 # levels. The idea here is that if a quantum session A is not identical to the
501 # environment session B, there have been no gates applied within that
502 # environment so far (otherwise merging would have occured). Thus, all data of A
503 # belongs into the original_data attribute of the environment with the highest
504 # level environment, where the environment quantum session isn't identical to A.
505 flattened_qubits = []

File ~\Documents\GitHub\Qrisp\src\qrisp\core\quantum_session.py:486, in QuantumSession.append..check_alloc(input, res)
484 if isinstance(input, list):
485 for item in input:
--> 486 check_alloc(item)
487 else:
488 if not input.allocated:
489 # pass

File ~\Documents\GitHub\Qrisp\src\qrisp\core\quantum_session.py:490, in QuantumSession.append..check_alloc(input, res)
487 else:
488 if not input.allocated:
489 # pass
--> 490 raise Exception(
491 f"Tried to perform operation {operation.name} on "
492 f"unallocated qubit {input}"
493 )

Exception: Tried to perform operation cswap on unallocated qubit qbl_400.0
}

[positr0nium]

Hi Diego,
I fixed the issue within 46bdb97 . Your code unfortunately has more problems. The QuantumVariables res and r are allocated within the function and are not being uncomputed. This should however be managable by allocating res and r prior to the conjugation and replacing the line r = p - r with an in-place function.

[positr0nium]

The following in-place function should do :)

from qrisp import *

# Performs a modular inplace right subtraction, ie.
# r = p - r
def inpl_rsub(r, p):
    x(r)
    r.inpl_adder(r.modulus+1, r)
    r += p

# Test function for a variety of inputs
for n in [5, 7, 13, 17, 19]:
    for p in range(n):
        
        r = QuantumModulus(n)
        
        h(r)
        init_r = r.duplicate(init = True)
        
        inpl_rsub(r, p)
        
        mes_res = multi_measurement([init_r, r])
        
        for init_r, r in mes_res.keys():
            if init_r is np.nan:
                continue
            if (p - init_r)%n != r:
                print(f"Adder failed for input constellation r = {init_r}, p = {p}")
                raise

[diehoq]

Thank you for the fix. I get what you mean for the QuantumVariable res, but r is indeed uncomputed within the algorithm. Do you mean something else?

[positr0nium]

With the line
r = r - p
You create a new QuantumVariable and call it r. The reference to the previous r is lost. The new r is uncomputed, while the old r stays alive. You can fix it by using the in-place function that I gave, because it doesn't create a new QuantumVariable

[diehoq]

Ah yes, indeed, and in this case you won't need to allocate it prior the conjugation