The complexity class QMA, defined by Watrous, in 2000, is the quantum
analogue of MA, defined by Babai, in 1985, which, in turn, is a generalization
of the class NP. The class MA generalizes the class NP in the sense that the
verification procedure of the purported proof, put forth by the prover, is
carried out by a probabilistic machine, rather than a deterministic one—as
the definition of the class NP demands.
In 2014, Grilo, Kerenidis, and Sikora, proved that the quantum proof, in
the setting of QMA, may always be replaced by, an appropriately defined,
quantum subset state—without any conceptual loss. That is, QMA ⊆ SQMA.
Grilo et al., named their new class SQMA, for subset-state quantum MerlinArthur.
Thus, one could write that SQMA = QMA, as the inclusion SQMA ⊆
QMA holds trivially.
After this result, by Grilo, Kerenidis, and Sikora, Fefferman and Kimmel, in
2015, used this new characterization of QMA, and further proved that there
exists some quantum oracle A—similar to that Aaronson and Kuperberg
introduced, and used, in 2006, to show that QMAA
1 6⊆ QCMAA—which is
such that QMAA = SQMAA 6⊆ QCMAA. Here, QCMA is that version of QMA,
defined by Aharonov, and Naveh, in 2002, in which the purported proof
is purely-classical, that is, a bitstring, and QMA1 is the perfect completeness
version of QMA. In their separation, Fefferman and Kimmel introduced, and
used, an interesting template to obtain oracle separations against the class
Drawing upon this recent result, by Fefferman and Kimmel, we prove that
there exists some quantum oracle A, such that SQMAA
1 6⊆ QCMAA. We
note that the class SQMA1 is the perfect completeness version of the class
SQMA. In our proof, we used the template of Fefferman and Kimmel, a
modified version of their basic quantum oracle construction, as well as
the basic decision problem, that they themselves used for their separation.
Note that our result implies that of Fefferman and Kimmel, as the inclusion
SQMA1 ⊆ SQMA holds.
After we state and prove our result, we take a detour to explore a bit the
world of oracle separations, both in the classical and the quantum setting.
That is, we explore some results, and their underlying methods, about
classical and quantum oracles being employed for proving separations—
about classical, or quantum, complexity classes. Hence, we investigate
some gems pertaining to the, not few at all, nor uninteresting, privileged
Finally, we return, to the research setting, to approach the open question
of whether there exists some classical, or quantum, oracle A, such that
1 6⊆ SQMAA
, or not. We record our efforts, and some of our first ideas,
Quantum computational complexity theory, computational complexity theory, relativized worlds, oracle separations, oracles, QMA, QCMA, SQMA, SQMA1, quantum states, quantum subset-states, quantum proofs, veri- fication procedures, verification protocols, diagonalization, and query complexity