Successful protocols for quantum information processing and quantum computation depend on the reliable storage and manipulation of the quantum state of a qubit. Qubits, however, are prone to errors because complete isolation from the environment is not possible. Methods for correcting these errors must also contend with the fact that direct measurement of a qubit destroys it. Xue et al. describe a repetitive quantum nondemolition method on a two-qubit system in which the state of the main qubit is mapped onto a second qubit that acts as an ancilla. Repeated measurement of the ancilla qubit allows the main qubit to be maintained and read out with higher fidelity.
They are billed as machines that will change the future, but quantum computers themselves are still in the future. All the same, scientists have been working on developing a working quantum computer for years now, and the frenzied competition to be the first has yielded a new record -- a 53-qubit quantum simulator.
From afar, it looks like a steampunk chandelier. It is, in fact, one of the most sophisticated quantum computers ever built. The processor inside has 50 quantum bits, or qubits, that process tasks in a (potentially) revolutionary way. Normally, information is created and stored as a series of ones and zeroes. Qubits can represent both values at the same time (known as superposition), which means a quantum computer can theoretically test the two simultaneously. Add more qubits and this hard-to-believe computational power increases.
At the forefront of this is IBM, who recently announced that they would connect up a quantum computer to the web and allow us to play with it. The project involves a 5 qubit machine, with a qubit allowing it to operate in both '0 and 1' states at the same time, thus increasing its potential computational power enormously. A one qubit machine has roughly 16 possible states, but once you get over 300, you begin to exceed the number of atoms in the universe.
Mechanical objects have important practical applications in the fields of quantum information and metrology as quantum memories or transducers for measuring and connecting different types of quantum systems. Here, we experimentally demonstrate a high-frequency bulk acoustic wave resonator that is strongly coupled to a superconducting qubit using piezoelectric transduction with a cooperativity of 260. Our device requires only simple fabrication methods and provides controllable access to a multitude of phonon modes. We demonstrate quantum control and measurement on gigahertz phonons at the single-quantum level.