01879nas a2200205 4500008003900000022001400039245004500053210004500098300001100143490000700154520131600161100001901477700002001496700002601516700002001542700001901562700002101581700001901602856005201621 2017 d a1367-263000aFlexible resources for quantum metrology0 aFlexible resources for quantum metrology a0630440 v193 aQuantum metrology offers a quadratic advantage over classical approaches to parameter estimation problems by utilising entanglement and nonclassicality. However, the hurdle of actually implementing the necessary quantum probe states and measurements, which vary drastically for different metrological scenarios, is usually not taken into account. We show that for a wide range of tasks in metrology, 2D cluster states (a particular family of states useful for measurement-based quantum computation) can serve as flexible resources that allow one to efficiently prepare any required state for sensing, and perform appropriate (entangled) measurements using only single qubit operations. Crucially, the overhead in the number of qubits is less than quadratic, thus preserving the quantum scaling advantage. This is ensured by using a compression to a logarithmically sized space that contains all relevant information for sensing. We specifically demonstrate how our method can be used to obtain optimal scaling for phase and frequency estimation in local estimation problems, as well as for the Bayesian equivalents with Gaussian priors of varying widths. Furthermore, we show that in the paradigmatic case of local phase estimation 1D cluster states are sufficient for optimal state preparation and measurement.1 aFriis, Nicolai1 aOrsucci, Davide1 aSkotiniotis, Michalis1 aSekatski, Pavel1 aDunjko, Vedran1 aBriegel, Hans, J1 aDür, Wolfgang uhttp://stacks.iop.org/1367-2630/19/i=6/a=06304400795nas a2200157 4500008003900000245007000039210006900109260000800178300000700186490000600193520031700199100002600516700001900542700002000561856005600581 2017 d00aMacroscopic superpositions require tremendous measurement devices0 aMacroscopic superpositions require tremendous measurement device cnov a340 v13 aMichalis Skotiniotis, Wolfgang Dür, and Pavel Sekatski, Quantum 1, 34 (2017). https://doi.org/10.22331/q-2017-11-21-34 We consider fundamental limits on the detectable size of macroscopic quantum superpositions. We argue that a full quantum mechanical treatment of system plus measurement device is required,…1 aSkotiniotis, Michalis1 aDür, Wolfgang1 aSekatski, Pavel uhttps://quantum-journal.org/papers/q-2017-11-21-34/00827nas a2200169 4500008003900000245005700039210005700096260000800153300000700161490000600168520033800174100002000512700002600532700002400558700001900582856005600601 2017 d00aQuantum metrology with full and fast quantum control0 aQuantum metrology with full and fast quantum control csep a270 v13 aPavel Sekatski, Michalis Skotiniotis, Janek Kołodyński, and Wolfgang Dür, Quantum 1, 27 (2017). https://doi.org/10.22331/q-2017-09-06-27 We establish general limits on how precise a parameter, e.g. frequency or the strength of a magnetic field, can be estimated with the aid of full and fast quantum control. We consider uncorr…1 aSekatski, Pavel1 aSkotiniotis, Michalis1 aKołodyński, Janek1 aDür, Wolfgang uhttps://quantum-journal.org/papers/q-2017-09-06-27/00480nas a2200145 4500008004100000245007800041210006900119300000700188490000700195100001600202700002200218700001900240700002100259856005400280 2007 eng d00aWeighted graph states and applications to spin chains, lattices and gases0 aWeighted graph states and applications to spin chains lattices a aS10 v401 aHartmann, L1 aCalsamiglia, John1 aDür, Wolfgang1 aBriegel, Hans, J uhttp://www.iop.org/EJ/abstract/0953-4075/40/9/S0101201nas a2200193 4500008004100000245006800041210006700109260001200176300001100188490000700199520063100206653003000837653001300867100002200880700001600902700001900918700002100937856004900958 2005 eng d00aSpin Gases: Quantum Entanglement Driven by Classical Kinematics0 aSpin Gases Quantum Entanglement Driven by Classical Kinematics c10/2005 a1805020 v953 aA spin gas is a natural extension of a classical gas. It consists of a large number of particles whose (random) motion is described classically, but, in addition, have internal (quantum mechanical) degrees of freedom that interact during collisions. For specific types of quantum interactions we determine the entanglement that occurs naturally in such systems. We analyze how the evolution of the quantum state is determined by the underlying classical kinematics of the gas. For the Boltzmann gas, we calculate the rate at which entanglement is produced and characterize the entanglement properties of the equilibrium state.10aentanglement distribution10aspin gas1 aCalsamiglia, John1 aHartmann, L1 aDür, Wolfgang1 aBriegel, Hans, J uhttp://link.aps.org/abstract/PRL/v95/e180502