cuStateVec issue on GPU in Google Colab

[95-martin-orion]

Branched from #495. @Gopal-Dahale wrote:

New problem that I faced when using qsimcirq as backend in tfq.ControlledPQC.

circuit  # some cirq circuit
observable # some observable
gpu_options = qsimcirq.QSimOptions(use_gpu=True, gpu_mode=1)
qsim_simulator = qsimcirq.QSimSimulator(qsim_options=gpu_options)

computation_layer = tfq.layers.ControlledPQC(circuit, observable,backend = qsim_simulator)

ValueError: cuStateVec GPU execution requested, but not supported. 
If your device has GPU support and the NVIDIA cuStateVec library is installed, you may need to compile qsim locally.

I have put the cuquantum files in /usr/local/cuquantum and in .bashrc have added these lines

export CUQUANTUM_ROOT=/usr/local/cuquantum
export LD_LIBRARY_PATH=${CUQUANTUM_ROOT}/lib:${LD_LIBRARY_PATH}
export CUQUANTUM_DIR=/usr/local/cuquantum

followed by source ~/.bashrc. Ran the test program given on docs site (statevec_example) which gave the result example PASSED.

Any solution for this would be helpful.

[95-martin-orion]

@Gopal-Dahale, can you confirm that you set up both cuQuantum and NVCC on your device before building qsim? The error you are seeing occurs when the qsim_custatevec is not initialized, which occurs if either cuQuantum or NVCC is not available when qsim is initially built.

Relevant code snippets:

qsim/pybind_interface/decide/decide.cpp

Lines 84 to 86 in f0216dd

	int detect_custatevec() {
	#if defined(__NVCC__) && defined(__CUSTATEVEC__)
	GPUCapabilities gpu = CUSTATEVEC;

qsim/qsimcirq/__init__.py

Lines 42 to 43 in f0216dd

	def _load_qsim_custatevec():
	instr = qsim_decide.detect_custatevec()

[Gopal-Dahale]

@95-martin-orion This issue is resolved for me. Here are the steps that helped me and can be used on google colab.

1. Download the tarball of cuquantum and extract it to /usr/local/cuquantum.
2. Set the following environment variables

import os
os.environ['CUQUANTUM_ROOT']='/usr/local/cuquantum'
os.environ['CUQUANTUM_DIR']='/usr/local/cuquantum'
os.environ['LD_LIBRARY_PATH']=f"/usr/local/cuquantum/lib:{os.environ['LD_LIBRARY_PATH']}"
os.environ['PATH']=f"/usr/local/cuquantum/lib:{os.environ['PATH']}"

3. Verify cuquantum installation by executing the code example.
4. Install qsimcirq.
5. Verify qsimcirq installation and its integration with cuquantum by executing the example with these options.

I think we can close this issue.

[QuantumJaeYoo]

FYI, from 0.16.0, qsim uses CUQUANTUM_ROOT only, no more CUQUANTUM_DIR.