The question whether quantum mechanics is complete and the nature of the transition between quantum mechanics and classical mechanics have intrigued physicists for decades. There have been many experimental breakthroughs in creating larger and larger quantum superposition and entangled states since Erwin Schrödinger proposed his famous thought experiment of putting a cat in a superposition of both alive and dead states in 1935. Remarkably, recent developments in quantum optomechanics and electromechanics may lead to the realisation of quantum superposition of living microbes soon. Recent evidence also suggests that quantum coherence may play an important role in several biological processes. In this review, we first give a brief introduction to basic concepts in quantum mechanics and the Schrödinger’s cat thought experiment. We then review developments in creating quantum superposition and entangled states and the realisation of quantum teleportation. Non-trivial quantum effects in photosynthetic light harvesting and avian magnetoreception are also discussed. At last, we review recent proposals to realise quantum superposition, entanglement and state teleportation of micro-organisms, such as viruses and bacteria.
The question whether quantum mechanics is complete and the nature of the transition between quantum mechanics and classical mechanics have intrigued physicists for decades. There have been many experimental breakthroughs in creating larger and larger quantum superposition and entangled states since Erwin Schrödinger proposed his famous thought experiment of putting a cat in a superposition of both alive and dead states in 1935. Remarkably, recent developments in quantum optomechanics and electromechanics may lead to the realisation of quantum superposition of living microbes soon. Recent evidence also suggests that quantum coherence may play an important role in several biological processes. In this review, we first give a brief introduction to basic concepts in quantum mechanics and the Schrödinger’s cat thought experiment. We then review developments in creating quantum superposition and entangled states and the realisation of quantum teleportation. Non-trivial quantum effects in photosynthetic light harvesting and avian magnetoreception are also discussed. At last, we review recent proposals to realise quantum superposition, entanglement and state teleportation of micro-organisms, such as viruses and bacteria.
The most striking feature of quantum mechanics is the existence of superposition states, where an object appears to be in different situations at the same time. The existence of such states has been previously tested with small objects, such as atoms, ions, electrons and photons (Zoller et al 2005 Eur. Phys. J. D 36 203–28), and even with molecules (Arndt et al 1999 Nature 401 680–2). More recently, it has been shown that it is possible to create superpositions of collections of photons (Deléglise et al 2008 Nature 455 510–14), atoms (Hammerer et al 2008 arXiv:0807.3358) or Cooper pairs (Friedman et al 2000 Nature 406 43–6). Very recent progress in optomechanical systems may soon allow us to create superpositions of even larger objects, such as micro-sized mirrors or cantilevers (Marshall et al 2003 Phys. Rev. Lett. 91 130401; Kippenberg and Vahala 2008 Science 321 1172–6; Marquardt and Girvin 2009 Physics 2 40; Favero and Karrai 2009 Nature Photon. 3 201–5), and thus to test quantum mechanical phenomena at larger scales. Here we propose a method to cool down and create quantum superpositions of the motion of sub-wavelength, arbitrarily shaped dielectric objects trapped inside a high-finesse cavity at a very low pressure. Our method is ideally suited for the smallest living organisms, such as viruses, which survive under low-vacuum pressures (Rothschild and Mancinelli 2001 Nature 406 1092–101) and optically behave as dielectric objects (Ashkin and Dziedzic 1987 Science 235 1517–20). This opens up the possibility of testing the quantum nature of living organisms by creating quantum superposition states in very much the same spirit as the original Schrödinger's cat 'gedanken' paradigm (Schrödinger 1935 Naturwissenschaften 23 807–12, 823–8, 844–9). We anticipate that our paper will be a starting point for experimentally addressing fundamental questions, such as the role of life and consciousness in quantum mechanics.
Abstract The lines separating Biology and Physics have started to blur in recent decades, leading to the emergence of the interdisciplinary field known as quantum Biology. This field looks into the possibility that basic quantum mechanical phenomena such as coherence, entanglement, tunneling, and superposition play crucial roles in biological processes that are beyond the scope of classical Physics. Biology has traditionally worked within the parameters of classical mechanics, presuming that delicate quantum effects cannot endure in the warm, humid, and cacophonous environments of living systems. But new findings in fields like photosynthesis, olfaction, avian magnetoreception, and enzyme catalysis indicate otherwise, suggesting that living things intentionally and possibly advantageously use quantum principles. From the earliest speculative theories to the most recent experimental confirmations, this book chapter methodically examines the evolution of quantum Biology. We investigate how the exceptionally high energy transfer efficiency in photosynthetic complexes particularly in the light-harvesting proteins of green sulfur bacteria and plants is supported by quantum coherence. The remarkable speed of proton transfers and enzymatic reactions during DNA replication is also investigated in relation to quantum tunneling. The chapter explores magnetoreception in migratory birds and suggests models in which sensitivity to Earth's geomagnetic field is made possible by radical pair mechanisms influenced by quantum entanglement. We also discuss the intriguing but controversial idea that quantum vibrations improve the human olfactory system's capacity for discrimination. In addition to examining particular occurrences, this research challenges more general theoretical models that seek to balance quantum mechanics with the decoherence commonly observed in biological settings. Recent developments in quantum information theory, biomimetic quantum technologies, and ultrafast spectroscopy are highlighted as essential instruments advancing empirical research. We also critically evaluate the field's methodological difficulties, the skepticism of overly optimistic interpretations, and the significant philosophical ramifications of acknowledging life as a quantum phenomenon. In conclusion, quantum Biology suggests that quantum effects are not uncommon aberrations but rather are an essential part of life, offering not only a fresh perspective for reinterpreting well-known biological processes but also the potential for a fundamental paradigm shift. Quantum biology has the potential to completely transform biotechnology, medicine, and our comprehension of consciousness and the origin of life as experimental methods advance. This chapter highlights the significance of interdisciplinary cooperation in order to completely comprehend the latest discoveries and possible future paths of quantum Biology, highlighting its revolutionary influence on our comprehension of life at the most basic levels. Key words: Quantum Biology, tunneling, avian magnetoreception, enzyme catalysis
The founders of quantum physics used to analyse thought experiments, to discuss state superposition, complementarity and entanglement. They imagined manipulating single particles, such as electrons, atoms or photons; they would be surprised to see that experiments with isolated atoms, molecules or photons are now carried on in many laboratories throughout the world. In our Cavity Quantum Electrodynamics (CQED) studies, we stabilize and count photon number states in the cavity. We also prepare and reconstruct photonic superposition states suspended between different 'classical realities', generating a laboratory version of Schrodinger famous 'Cat', which he had imagined to be simultaneously dead and alive. We have also investigated the decoherence process, which explains the transition between the quantum and the classical worlds. CQED physics has recently been extended to artificial 'atoms' made from superconductors, in a new domain of mesoscopic physics called Circuit QED. This development opens the way to applications in quantum information science.
In quantum theory, a particle is allowed to be in a state of coherent superposition among a set of orthogonal states. A vivid picture of this concept is the “Schrödinger cat”: a cat is alive and dead simultaneously. This would be no surprise if one means a large number of an ensemble of cats with 50% alive and 50% dead. But, “Schrödinger cat” is a cat. People are talking about a cat being alive and dead simultaneously. In mathematics, the best word to characterize the relationship between states “alive” and “dead” is perhaps “orthogonal”. In quantum mechanics, the superposition of orthogonal states is used to describe the state of a quantum object, or a particle. The superposition principle is indeed a mystery compared to our everyday classical life experience. Beyond the superposition of orthogonal single-particle states, the superposition of orthogonal multi-particle states represents an even more troubling concept in classical theory.
Abstract This paper, intended for a general audience, contains a description of Erwin Schrödinger’s thought experiment which was designed to show the strange results of extending the formalism of quantum theory, particularly the idea of superposition, beyond the subatomic regime. A way of understanding superposition in the terms of formal logic is outlined. The development of Schrödinger’s ideas after this thought experiment is traced along with a brief description of some work which realises it in actual experiments, as well as proposals for taking it further.
Abstract In this chapter, the notion of quantum superposition of states is introduced through the example of a polarized photon. This brings out the novel feature that the state of the system depends on how the experiment is set up. The paradoxical consequences of quantum superposition, such as that a cat can be simultaneously dead and alive, are also discussed. This is the essence of the famous Schrödinger’s cat paradox. This description motivates another important consequence of quantum mechanical description of multiple objects; namely, their ability to exist in an entangled state. The properties of the two objects can remain entangled no matter how far away they are from each other and thus have the ability to influence each other. After discussing these aspects of quantum mechanics, the application of quantum entanglement to novel phenomena of quantum teleportation and quantum computing are presented.