code: public FullColumnDescription getQuantumDescription()
      {
          if (quantumField == null)
          {
              for (FullColumnDescription fd: getPartitionKeyColumnDescriptions())
              {
                  if (fd.hasQuantum())
                  {
                      if (quantumField != null)
                      {
                          throw new IllegalStateException("Table definition has more than one quantum.");
                      }
                      else
                      {
                          quantumField = fd;
                      }
                  }
              }
          }
  
          return quantumField;
      }
docs: Get the FullColumnDescription for a quantum field, if any.
  @return null if there is no quantum information