Expected Behavior

Should work.

Current Behavior

Quantum volume circuits constructed using the method from the recent blog post:

https://www.ibm.com/blogs/research/2018/05/quantum-circuits/

fail to compile on the ibmqx5 backend with the error:

MapperError: 'swap_mapper failed: layer X, sublayer Y, "cx q[0],q[9];\n"'

where X and Y depend on the number of qubits and depth of the circuit. However, the error is always with respect to a cx between qubits 0 and 9. The error occurs only when the number of qubits is not n=16, which is the max for the ibmqx5. For example n=16, depth=11 is successful, but n=15, depth=11 fails. Others like n=10, depth=5 also fail with the same error, while n=16, depth=5 works.

Possible Solution

Steps to Reproduce (for bugs)

Run the code with the above mentioned examples.

Context

Your Environment

QISKit 0.5, OSX