Sensitivity and entanglement in the avian chemical compass

Abstract

The Radical Pair Mechanism can help to explain avian orientation and navigation. Some evidence indicates that the intensity of external magnetic fields plays an important role in avian navigation. In this paper, based on a two-stage strategy, we demonstrate that birds could reasonably detect the directions of geomagnetic fields and gradients of these fields using a yield-based chemical compass that is sensitive enough for navigation. Also, we find that the lifetime of entanglement in this proposed compass is angle-dependent and long enough to allow adequate electron transfer between molecules.Introduction. -The navigational ability of birds has been a subject of interest for centuries. Every year migrant birds fly hundreds to thousands of miles between their seasonal habitats. Researchers have been trying to explain this astonishing phenomenon for decades. The radical pair mechanism (RPM) is a promising hypothesis to explain this extraordinary phenomenon [1][2][3][4][5]. This RPM was first proposed by Schulten et al. based on the fact that low magnetic fields can alter the rates and the yields of photochemical reactions [1]. This mechanism has been supported by a series of behavioral experiments [6][7][8][9][10], which indicate that the avian compass depends on both inclination and light intensity. Also, the photoreceptor cryptochrome located in the avian retina is involved in this hypothesis [11][12][13][14][15][16][17][18][19].Both theoretical and experimental studies have revealed that the internal anisotropic hyperfine interaction is the key factor for a radicalpair-based compass to detect the presence of an external magnetic field and its direction [1], [20][21][22][23][24][25]. The hyperfine interaction has been modeled and simulated in order to understand how to optimize the sensitivity of the chemical compass [26]. Also, the role of quantum coherence and entanglement in the chemical compass has

Upper bound on the biological effects of 50/60 Hz magnetic fields mediated by radical pairs

“…First, when a radical pair is formed in a singlet state, but not when it is formed as an unpolarized triplet, its electron spins are entangled (88). The possibility that entanglement arises naturally in the 'warm, wet and noisy' milieu of a living cell has attracted a certain amount of attention from theoretical physicists (89)(90)(91)(92)(93)(94). Nevertheless, there is no apparent way in which this entanglement can enhance magnetic responses (24).…”

The quantum needle of the avian magnetic compass

“…In support of this proposal, the photochemistry of isolated cryptochromes in vitro has been found to respond to applied magnetic fields in a manner that is quantitatively consistent with the radical pair mechanism (15). Aspects of the radical pair hypothesis have also been explored in a number of theoretical studies, the majority of which have concentrated on the magnitude of the anisotropic magnetic field effect (9,10,16,17,(19)(20)(21)(22)(23)(24)(25)(26)(27). Very little attention has been devoted to the matter we address here: the precision of the compass bearing available from a radical pair sensor (28).…”

“…A crucial element in all such calculations is the presence of nuclear spins whose hyperfine interactions are the source of the magnetic anisotropy (8,16). Most studies have focused on idealized spin systems comprising the two electron spins, one on each radical, augmented by one or two nuclear spins (9,(21)(22)(23)(24)(25)(26)(27)34). Only a handful has attempted to deal with realistic, multinuclear radical pairs (10,16,17,20).…”

“…Several studies have assumed, explicitly or implicitly, that the spin coherence persists for about a microsecond, i.e., the reciprocal of the electron Larmor frequency (1.4 MHz) in a 50-μT field (9,10,17,20). Either because the spin system was grossly oversimplified (9,(21)(22)(23)(24)(25)(26)(27)34), or because of this restriction on the spin coherence time, previous theoretical treatments have generally predicted the reaction yield to be a gently varying (often approximately sinusoidal) function of the orientation of the radical pair in the geomagnetic field. Although capable of delivering information on the direction of the field, such a compass would not provide a precise heading.…”

The radical pair mechanism and the avian chemical compass: Quantum coherence and entanglement

“…In this section, we will introduce some of our work on the topic of the radical pair mechanism . We investigate two aspects of the radical pair mechanism: the yields of defined signal states and the entanglement of the states.…”