Browse Physics

A quantum algorithm that uses the solution to a set of linear equations provides an exponential speedup by comparison with classical alternatives.

An entangled state of six photons could potentially carry quantum information over large distances and between different reference frames.

A theoretical analysis of recent experiments suggests that a key feature of a topological quantum computer—the unusual statistics of quasiparticles in the quantum Hall effect—may finally have been observed.

Researchers have measured the overlap time of an entangled pair of photons by treating them like ordinary laser pulses.

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.

The demonstration of all-optical spin-echo measurements may provide a route toward decoupling spins from noise sources.

A system familiar in condensed matter—particles on a hexagonal lattice—could be a useful initial state for a one-way quantum computer.

A miniature time machine, possibly based on a wormhole through spacetime, could be used to break a super-secure quantum code.

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.

Loading cold atoms into a hollow-core optical fiber enables all-optical switching with just several hundred photons.

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.

Entanglement may not be the source of a quantum computer’s power. But if not, what is?

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?

Two theoretical studies reveal how one might achieve electric-field control of spin in semiconductors, both in an impurity-localized electron, and also with a quantum dot molecule.

A rigorous estimate shows that an error correction code for a scalable quantum computer can accommodate error at the 0.1% level—about ten times more tolerant than most other methods.

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.