Problem with products of boson.number operator in latest CUDA-Q

[chnixi]

Hello,

When I am trying to run a multi-body dynamics simulation with the latest CUDA-Q version 0.12, I get an error whenever the Hamiltonian contains a product of two boson.number operators for the 3rd qubit and beyond, for example boson.number(index)*boson.number(index) where index>=2. The error message reads “Error in tensor callback: missing dimension for degree
#ERROR: Exception: #ERROR(CallbackError): External tensor callback function failed with error code 14
RuntimeError: [cudaq] %16 in computeImpl (line 92)”

No such error occurs for qubit index=0,1, or just the number operator itself (without product). The same simulation runs without issues on the older 0.10 version. Below is an example script to reproduce the error:

import numpy as np
import cudaq
from cudaq import boson, Schedule, ScipyZvodeIntegrator, spin, RungeKuttaIntegrator
import cupy as cp
import matplotlib.pyplot as plt

L=5
Nmax=1
cudaq.set_target("dynamics")

init=np.zeros(np.power(Nmax+1,L))
init[0]=1

index=1
hamiltonian = boson.number(index)*boson.number(index)

for i in range(L-1):
  hamiltonian = hamiltonian + boson.identity(i)

dimensions={}
for i in range(L):
   dimensions[i] = Nmax+1
rho0 = cudaq.State.from_data(
       cp.array(init , dtype=cp.complex128))

t_final=25
n_steps=105
# Schedule of time steps.
steps = np.linspace(0, t_final, n_steps)
schedule = Schedule(steps, ["t"])

# Run the simulation.
evolution_result = cudaq.evolve(hamiltonian,
                          dimensions,
                          schedule,
                          rho0,
                          observables=[],
                          collapse_operators=[],
                          store_intermediate_results=True)

get_result = lambda idx, res: [
    exp_vals[idx].expectation() for exp_vals in res.expectation_values()
]

[1tnguyen]

Hi @chnixi,

This is a bug in CUDA-Q 0.12 that we have identified and fixed (for more details, see here).

Could you please try the CUDA-Q nightly Docker image (nvcr.io/nvidia/nightly/cuda-quantum:cu12-latest) to check if it works for you?

[chnixi]

OK, I am using the latest docker image updated on August 20 here. Unfortunately I am still getting the same error for index=3 (but not for index=1,2) which reads "Error in tensor callback: missing dimension for degree 3
#ERROR: Exception: #ERROR(CallbackError): External tensor callback function failed with error code 14
RuntimeError: [cudaq] %16 in computeImpl (line 92)".

[1tnguyen]

The link above is for the versioned/released Docker images.

Could you please try the nightly channel, https://catalog.ngc.nvidia.com/orgs/nvidia/teams/nightly/containers/cuda-quantum/tags?