 Notwithstanding the excitement around the discovery of Shor’s algorithm, and putting aside the presently insurmountable problem of practically realising and implementing a large scale quantum computer, a crucial theoretical question remains open: What physical resources are responsible for quantum computing’s putative power? Put another way, what are the essential features of quantum mechanics that would in principle allow one to solve problems or simulate certain systems more efficiently than on a classical computer? A number of candidates have been put forward. Fortnow (2003) posits interference as the key, though it has been suggested that this is not truly a quantum phenomenon (Spekkens 2007). Jozsa (1997) and many others point to entanglement, although there are purported counter-examples to this thesis (see, e.g., Linden and Popescu (1999), Gottesman (1999), Biham et al. (2004), and finally see Cuffaro (2017) for a philosophical discussion). Howard et al. (2014) appeal to quantum contextuality. For Bub (2010) the answer lies in the logical structure of quantum mechanics (cf. Pitowsky 1989). Duwell (2018) argues for quantum parallelism, and for Deutsch (1997) and Hewitt-Horsman (2009) it is “parallel worlds” which are the resource.