Phys. Rev. Focus24, 7 (2009) – Published August 17, 2009
Real-world events always proceed in the direction of increasing entropy, even though the laws of physics don’t require it. The reason we never see events that reduce entropy is that they cannot leave behind any evidence of having happened, according to a new theory.
This design of atomic quantum memory tells us when a pulse of light has been successfully stored and then proceeds to retrieve it without significantly affecting its polarization. The exquisite operation provides a new capability for quantum information networks.
A proposal for obtaining optical resolution better than the classical limit by means of spatially entangled quantum states of light opens a new frontier in the fields of quantum optical imaging, metrology, and sensing.
Coherent optical systems combined with micromechanical devices may enable development of ultrasensitive force sensors and quantum information processing technology, as well as permit observation of quantum behavior in large-scale structures.
A new algorithm allows for the extremely efficient calculation of thermally averaged quantities in one dimension, in conjunction with the density matrix renormalization group method. The key is the judicious selection of a few representative states.
Creating a practical solid-state quantum computer is seriously hard. Getting such a computer to operate at room temperature is even more challenging. Is such a quantum computer possible at all? If so, which schemes might have a chance of success?
Preparing a harmonic oscillator in a state with a well-defined energy is a tricky business. With the new tools provided by cavity and circuit quantum electrodynamics it is now possible to make these pure quantum states and watch how they evolve in time.
Large-scale quantum computers are hard to construct because quantum systems easily lose their coherence through interaction with the environment. Researchers have tried to avoid this problem by using geometric phase shifts in the design of quantum gates to perform information processing. Experiments and simulations have shown that these gates may be tolerant to certain types of faults, and may therefore be useful for robust quantum computation.
Quantum measurements are conventionally thought of as irretrievably “collapsing” a wave function to the observed state. However, experiments with superconducting qubits show that the partial collapse resulting from a weak continuous measurement can be restored.
Squeezed states can enhance the sensitivity of a detector and the storage capability of quantum memory devices. Because these features improve with an increase in system size, researchers are exploring ways to produce squeezed states in large ensembles of atoms.
Spin decoherence is a fundamental obstacle in quantum computation and spintronics. Scientists show they can increase the lifetime of a localized spin in a diamond lattice up to 100 times by polarizing the surrounding spins on the lattice.