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Quantum Compass of Migratory Birds

substances such as large molecules and crystals. Tere has been active discussion in the feld of physics

and biophysics, and special articles have been published (Ball, 2011; Vedral, 2011). Tis feld has evolved

into a promising research area called “Quantum Biology” (Ball, 2011; Al-Khalili and McFadden, 2014;

Solov’yov et al., 2014).

Te possibility has emerged that multiple states such as singlet and triplet states are actually realized

in living organisms. It’s like a “Schrodinger’s bird” (Vedral, 2011). Tat is, in the eyes of migratory birds,

there is a “quantum entanglement,” in which the spin becomes zero as a whole, and it is thought that

when light is absorbed, the quantum entanglement collapses, and consequently, the GMF can be sensed

(Vedral, 2011). Vedral (2011) estimates that the quantum efect in the bird’s eye lasts for 100 µs. Te

duration of the quantum efect is surprisingly long since in the case of the artifcial electron system, the

duration of the quantum efect is usually shorter than 50 μs (Vedral, 2011). Te observation of long-lived

electronic quantum coherence in a photosynthetic light-harvesting system (Engel et al., 2007) has led to

much efort being devoted to the elucidation of the quantum mechanisms of the photosynthetic excita­

tion energy transfer (Ishizaki and Fleming, 2009; 2011; Ishizaki et al., 2010; Sarovar et al., 2010; Ishizaki

and Fleming, 2011). According to Vedral (2011), “We still don’t know how natural biological systems sus­

tain such a long-term quantum efect, but if we can elucidate the mechanism in detail, we will develop

a method to prevent quantum computers from being destroyed by decoherence.” In addition, together

with the photosynthesis of green sulfur bacteria, Oka (2015) anticipates that the study of the quantum

efect can be expected to provide insights that lead to the solution of energy problems.

What happens if an oscillating magnetic feld is applied in addition to the GMF? As shown in Figure

4.6, in actual migratory birds, the magnetic compass in the body does not function normally when

another oscillating magnetic feld including anthropogenic electromagnetic noise is applied in addition

to the GMF (Talau et al., 2005; Kavokin, 2009; Ritz et al., 2009; Wiltschko et. al., 2011; Engels et al., 2014;

Kavokin et al., 2014; Xu et al., 2014a; Hiscock et al., 2017). Tat is, the magnetic sensor exerts the function

of migration in a normal state, but it is considered that the magnetic sensor causes an abnormality in the

function in an environment accompanied by an electromagnetic abnormality.

Bojarinova et al. (2020) proposed that the RPM fails to explain the obtained results quantitatively;

the observed sensitivity thresholds of the magnetic compass to oscillating magnetic felds in European

robins and garden warblers are two orders of magnitude less than what the existing theory would give

even with the most liberal choice of parameters (Talau et al., 2005; Kavokin, 2009; Ritz et al., 2009;

Wiltschko et. al., 2011; Engels et al., 2014; Kavokin et al., 2014; Xu et al., 2014a; Hiscock et al., 2017).

Teir experiments have demonstrated the insensitivity of the bird magnetic compass to oscillating mag­

netic felds applied locally to the eyes (Bojarinova et al., 2020). Teir results do not necessarily deny

the key role of radical pair reactions in magnetoreception. However, it defnitely disproves the radical

pair model, which in particular suggests that: (1) magnetic sensitivity of photochemical reactions in

CRY molecules situated in the retina produces a visual image of the GMF, (2) the compass is disrupted

by oscillating magnetic felds due to its efect on electron spins in radical pairs formed by the CRY

(Bojarinova et al., 2020). If it were so, the magnetic-feld-induced image would have been destroyed by

the oscillating magnetic felds that we applied to the central part of the retina. Teir fndings, therefore,

point out the existence of other, so far unknown, components of the avian magnetoreception system

(Bojarinova et al., 2020).

Te light-dependent magnetic compass sense of the night-migratory European robin is thought to

rely on magnetically sensitive chemical reactions of radical pairs in cryptochromes (ErCRYs) located

in the birds’ eyes (Ritz et al., 2000; Zapka et al., 2009; Hore and Mouritsen, 2016; Xu et al., 2021). Ren

et al. (2021) have investigated the angular precision of the light-dependent compass sense of the night-

migratory European robin using the information theory approach devised by Hiscock et al. (2019). Te

information theory approach was developed that provides a strict lower bound on the precision with

which a bird could estimate its head direction using only geomagnetic cues and a CRY-based radical

pair sensor (Hiscock et al., 2019). Te leading hypothesis is that the GMF can alter the course of photo­

chemical reactions in the birds’ eyes even though the energies involved are a million times smaller than