Error while running Quantum Teleportation Algorithm on real device using qiskit on IBM-Q

Question

I am trying to implement Quantum Teleportation Algorithm on an actual device, I am using IBM-Q Jupyter notebook for the same purpose.

The code is as follows:

import qiskit as qk
from qiskit import ClassicalRegister, QuantumRegister, QuantumCircuit
from qiskit import execute, Aer
from qiskit import IBMQ
from qiskit.visualization import plot_histogram
%config InlineBackend.figure_format = 'svg'

def apply_secret_unitary(secret_unitary, qubit, quantum_circuit, dagger):
  functionmap = {
    'x': quantum_circuit.x,
    'y': quantum_circuit.y,
    'z': quantum_circuit.z,
    'h': quantum_circuit.h,
    't': quantum_circuit.t
  }
  if dagger == 1:
    functionmap['t'] = quantum_circuit.tdg

  if dagger:
    [functionmap[unitary](qubit) for unitary in secret_unitary]
  else:
    [functionmap[unitary](qubit) for unitary in secret_unitary[::-1]]

secret_unitary = 'hzxhzhx'

qc = QuantumCircuit(3, 1)
'''
qc[0] -> The qubit to be teleported
qc[1] -> entangled state, possessed by alice
qc[2] -> entangled state, possessed by bob
'''

apply_secret_unitary(secret_unitary, qc.qubits[0], qc, dagger = 0) 
qc.barrier()
qc.h(1)
qc.cx(1, 2)
qc.barrier()
qc.cx(0, 1)
qc.h(0)
qc.cx(1, 2)
qc.cz(0, 2)
apply_secret_unitary(secret_unitary, qc.qubits[0], qc, dagger = 1)
qc.barrier()
qc.measure(2, 0);
qc.draw(output= 'mpl')

IBMQ.load_account()
provider = IBMQ.get_provider(hub='ibm-q')
provider.backends()

from qiskit.providers.ibmq import least_busy
backend = least_busy(provider.backends(filters = lambda b: b.configuration().n_qubits >= 3 and 
                                       not b.configuration().simulator and 
                                       b.status().operational == True))
job_exp = execute(qc, backend = backend, shots = 8192)
exp_result = job_exp.result()

exp_measurement_result = exp_result.get_counts()
print(exp_measurement_result)
plot_histogram(exp_measurement_result)

The error which the following code gives is:

IBMQJobApiError: "'400 Client Error: Bad Request for url: https://api.quantum-computing.ibm.com/api/Network/ibm-q/Groups/open/Projects/main/Jobs/5e73033786653e0018a2364e/resultDownloadUrl. Cannot get presigned download url., Error code: 3202.'"

I've tried deleting my account and load a new account using a newly generated token but that doesn't seem to work either.

Clicking the link in the error gives the following error:

OPERATION_NOT_AVAILABLE
404 Shared class "Hub" has no method handling GET /ibm-q/Groups/open/Projects/main/Jobs/5e72ff01121d5e0018bfe775/resultDownloadUrl.
code: 2411

perhaps, I am using a method which is now deprecated. How can I tackle this situation?

Answer 1

I'm not sure what had caused the problem but I was able to solve it and most likely know what the problem was.

Consider these two lines from my code above:

job_exp = execute(qc, backend = backend, shots = 8192)
exp_result = job_exp.result()

Problem with the above lines is that we are not waiting for the actual quantum device to compute and send over the data. To avoid this, we can use a method called job_monitor from qiskit.tools.monitor which when called, let us know whether the job is complete or not.

After it displays that the job has successfully run we should expect value from result

Following is the code for the same purpose:

IBMQ.load_account()
provider = IBMQ.get_provider(hub = 'ibm-q')
backend = least_busy(provider.backends(filters = lambda x: x.configuration().n_qubits >= 3
                                      and not x.configuration().simulator
                                      and x.status().operational == True))
print('least busy backend: ', backend)

from qiskit.tools.monitor import job_monitor
job = execute(qc, backend = backend, shots = 8192)
job_monitor(job)

Proceed further only after the output to the above cell becomes 'Job Status: job has successfully run' which may take some time depending upon the value of shots.

After that, you can call result() and get_counts() to get the values:

result = job.result()
counts = result.get_counts()

Answer 2

EDIT: I believe this is solved in @IEIrodov's answer below.

I'm not sure what's causing the issue, but based on similar issues on the qiskit slack channel, I don't think it's something you're doing.

As a workaround, try running:

exp_result = job_exp.result()
exp_measurement_result = exp_result.get_counts()
print(exp_measurement_result)
plot_histogram(exp_measurement_result)

Separately in a new cell.

(also, if you're trying to verify teleportation, you need to apply_secret_unitary on line 42 to qc.qubits[2] instead of qc.qubits[0]).

Answer 3

Error 3202 is a networking error when trying to get the requested page. In this case the results for your job.