  The radical pair mechanism is an important model that may provide a basis for
biological magnetoreception. To account for the high orientation precision of
the real avian compass, P. J. Hore et al. proposed an intriguing phenomenon
called quantum needle [Proc. Natl. Acad. Sci. 113, 4634 (2016)], where a
spike-like feature emerges in the fractional yield signal. However, it is
believed that quantum needle requires the radical pair lifetime to be longer
than a few microseconds and thus poses stern challenges in realistic biological
systems. Here, we exploit the optimization techniques and find a novel class of
model system, which sustains much more prominent features of quantum needle and
significantly relaxes the requirement for radical pair lifetime. Even more
surprisingly, we find that the characteristics of quantum needle retain a
narrow functional window around the geomagnetic field, which is absent in the
previous model systems. Therefore, our work provides essential evidence for
identifying the possible physical mechanism for quantum needle in chemical
magnetoreception.
