  Quantum informatic quantities such as entanglement entropy are useful in
detecting quantum phase transitions. Recently, a new entanglement measure
called pseudo-entropy was proposed which is a generalization of the more
well-known entanglement entropy. It has many nice properties and is useful in
the study of post-selection measurements. In this paper, one of our goals is to
explore the properties of pseudo-entropy and study the effectiveness of it as a
quantum chaos diagnostic, i.e. as a tool to distinguish between chaotic and
integrable systems. Using various variants of the SYK model, we study the
signal of quantum chaos captured in the pseudo-entropy and relate it to the
spectral form factor (SFF) and local operator entanglement (LOE). We also
explore another quantity called the negativity of entanglement which is a
useful entanglement measure for a mixed state. We generalized it to accommodate
the transition matrix and called it pseudo-negativity in analogy to
pseudo-entropy. We found that it also nicely captures the spectral properties
of a chaotic system and hence also plays a role as a tool of quantum chaos
diagnostic.
