  Quantum private information retrieval (QPIR) is a protocol in which a user
retrieves one of multiple classical files by downloading quantum systems from
non-communicating $\mathsf{n}$ servers each of which contains a copy of all
files, while the identity of the retrieved file is unknown to each server.
Symmetric QPIR (QSPIR) is QPIR in which the user only obtains the queried file
but no other information of the other files. In this paper, we consider the
$(\mathsf{n} - 1)$-private QSPIR in which the identity of the retrieved file is
secret even if any $\mathsf{n} - 1$ servers collude, and derive the QSPIR
capacity for this problem which is defined as the maximum ratio of the
retrieved file size to the total size of the downloaded quantum systems. For an
even number n of servers, we show that the capacity of the
$(\mathsf{n}-1)$-private QSPIR is $2/\mathsf{n}$, when we assume that there are
prior entanglements among the servers. We construct an $(\mathsf{n} -
1)$-private QSPIR protocol of rate $\lceil\mathsf{n}/2\rceil^{-1}$ and prove
that the capacity is upper bounded by $2/\mathsf{n}$ even if any error
probability is allowed. The $(\mathsf{n} - 1)$-private QSPIR capacity is
strictly greater than the classical counterpart.
