  A two-step measurement protocol of a quantum system, known as weak value
(WV), has been introduced more than two decades ago by Aharonov et al. [1], and
has since been studied in various contexts. Here we discuss another two-step
measurement protocol which we dub null weak value (NWV). The protocol consists
of a partial-collapse measurement followed by quantum manipulation on the
system and finally a strong measurement. The first step is a strong measurement
which takes place with small probability. The second strong measurement is used
as postselection on the outcome of the earlier step. Not being measured in the
partial-collapse stage (null outcome) leads to a non-trivial correlation
between the two measurements. The NVW protocol, first defined for a two-level
system [2], is generalized to a multi-level system, and compared to the
standard-WV protocol.
