A complex in psychosis

Solomon H. Snyder
2008 Nature  
mGluR2 Agonist: stimulatory effect Antagonist: inhibitory effect LY341495 Potential antipsychotics LY379268 LY2140023 Antipsychotics (Atypical neuroleptics) Hallucinogens (LSD, DOI, mescaline) 2AR Psychotomimetic or antipsychotic actions about the function -its period -is contained in the input register. After some 'fiddling' , this period can be read out with many fewer operations than a classical computer requires 2 . (In a classical calculation we would have to run the computation many
more » ... once for each input value, to slowly, step by step, build up global information about the function.) Encoding this information in material quantum states, such as those of atomic clouds, is a particularly promising avenue towards implementing quantum-computational schemes: the interactions between atoms can be strong, and processing (through controlled changes to the quantum states) can happen fast. Long-distance transmission of the resulting output quantum states, on the other hand, works better with light: light can travel fast and with minimal losses in optical fibres. Reliable and efficient ways of mapping quantum information between light and matter are therefore an essential component of any quantum information network. In their experiments, Choi et al. 1 achieve this transfer using 'slow light' 3 . Under particular conditions dictated by quantum mechanics, the speed of a light pulse that has been injected into an atom cloud illuminated by a control laser can be reduced by many orders of magnitude. As the pulse slows, its spatial extent shrinks, and it ultimately fits snugly inside the atom cloud (Fig. 1) . The pulse affects the internal states of atoms within its localized region, creating a hologram-like imprint of itself in the atom cloud. If the control laser is turned off, the light pulse is halted and extinguished, but its atomic imprint remains in the cloud. If the control laser is turned back on, the same process runs backwards: the light pulse is regenerated and moves on, exits the atom cloud and speeds back up. Such storage of optical information has been demonstrated for classical light pulses containing many photons 4,5 and for single-photon light pulses 6,7 . The authors show that the entanglement of two light fields also survives such storage. They create their single-photon pulse by generating a single atomic excitation in a separate 'source' atom cloud, using the slow-light effect to read it out. The entangled optical modes generated at the beam splitter are injected into the main atomic sample, separated by 1 millimetre. After a microsecond, the authors are able to regenerate the optical fields. They then introduce a phase shift into one before the two modes recombine at a second beam splitter. Depending on the phase shift introduced, constructive or destructive quantum interference between the two optical paths is measured at a detector after the second beam splitter. The contrast of the fringes obtained as the phase is varied tells us the quality of the entanglement. So what is the next step? Separate control of the phase relationship between the two optical modes' input to the atom cloud would allow the controlled storage and revival of actual quantum bits. Choi et al. 1 use cold atoms for their NEUROSCIENCE The molecular basis of psychoses such as schizophrenia remains largely mysterious. The interaction between two of the brain receptors involved adds to evidence that will help in the search for explanations. This is a story that involves three types of receptor in the brain that influence human perception and behaviour (those for the neurotransmitters dopamine, serotonin and glutamate), and the drugs that block or enhance their activity. Such drugs are used by researchers to investigate the causes of psychotic disorders such as schizophrenia, and by clinicians to treat patients. Classical antipsychotic drugs, designated 'typical neuroleptics' , act predominantly by blocking dopamine D2 receptors. A new generation of more effective 'atypical neuroleptics' also blocks a subtype of serotonin receptor known as 5-HT 2A , or more simply as 2AR. And last year we had the promising report 1 of a drug that mimics the effect of glutamate at a subtype of one of its receptors, metabotropic glutamate receptor 2 (mGluR2), and that seems to be as effective as atypical neuroleptics. This is the background against which the paper by González-Maeso et al. 2 appears (page 93 of this issue): these authors show that experiments, laser cooled to about 125 microkelvin above absolute zero to avoid thermal smearing of the stored holographic imprints; but it would be interesting to cool things down further, forming the phase-coherent state of atomic matter known as a Bose-Einstein condensate, which offers much-increased possibilities for storage and controlled processing 8 . The storage of entangled optical fields in two separated atom clouds also needs to be formally demonstrated. Such entanglement would allow the efficient sharing of quantum keys for secure encryption 9 , and the transfer (teleportation) of quantum bits between two atomic clouds by simple transmission of pairs of classical bits 10 . Will any or all of this ever get to a stage at which it can be used in practical devices? That remains to be seen. We can state, however, that a century after quantum mechanics was discovered, the possibilities it offers continue to boggle our minds. ■ Lene Vestergaard Hau is in the Figure 1 | Receptor interaction. González-Maeso et al. 2 find that the metabotropic glutamate receptor 2 (mGluR2) and serotonin 5-HT 2A receptor (2AR) physiologically bind each other, leading to reciprocal regulation of their functions. Agonists that stimulate mGluR2 are antipsychotic, whereas 2AR agonists, such as hallucinogens, have the opposite effect. It is conceivable that the clinically significant antischizophrenic effects of LY2140023, an mGluR2 agonist 1 , derive from reducing the excessive -and hence hallucinogen-like -activity of 2AR. DOI, 2,5-dimethoxy-4iodoamphetamine. 38
doi:10.1038/452038a pmid:18322519 fatcat:xneqjqdx55hrpfp7wxigads64i