Attaining subclassical metrology in lossy systems with entangled coherent states

Abstract

Quantum mechanics allows entanglement enhanced measurements to be performed, but loss remains an obstacle in constructing realistic quantum metrology schemes. However, recent work has revealed that entangled coherent states (ECSs) have the potential to perform robust subclassical measurements [J. Joo et al., Phys. Rev. Lett. 107, 083601 (2011)]. Up to now no read-out scheme has been devised that exploits this robust nature of ECSs, but we present here an experimentally accessible method of achieving precision close to the theoretical bound, even with loss. We show substantial improvements over unentangled classical states and highly entangled NOON states for a wide range of loss values, elevating quantum metrology to a realizable technology in the near future.

Effect of multimode entanglement on lossy optical quantum metrology

“…Our scheme shows significant improvements over the SNL, the ECS with the measurement scheme in Ref. [62], and the NOON state (for most loss rates). We see that our scheme is much more robust than the NOON state, which is quickly destroyed when the transmission rate drops below η = 0.9.…”

“…(Color online) Our measurement scheme, δφ UCSM , comes close to the CRB for the UCS, δφ UCS , and shows large improvements over the ECS measurement scheme in Ref. [62], δφ ECSM . We see that our state surpasses the precision of the NOON state δφ NOON and the SNL δφ SNL for most loss rates.…”

“…A photonnumber resolving detector (PNRD) is then used to count the number of particles in the state ρ and a Bayesian scheme is used to infer the phase φ, and the precision with which it can be measured δφ (we explain this scheme in detail in Ref. [62]). PNRDs are an area of intense research [63], and devices that are highly sensitive in the low-photon regime, the area most relevant for this work, have been demonstrated [64][65][66].…”

Microtoroidal cavity QED with fiber overcoupling and strong atom-field coupling: A single-atom quantum switch for coherent light fields

“…That is, the atomic state becomes entangled with a coherent state pulse (of potentially quite large photon number, as shown in the previous section) propagating in either the forward or backward direction along the fiber. With a suitable (unitary) rotation and projective measurement of the atomic state, this system could therefore be used to prepare entangled coherent states, which are of significant interest in the contexts of, e.g., quantum information processing and quantum metrology [55][56][57][58]. However, such states are by nature extremely sensitive (i.e., fragile) to uncontrolled losses, which in the present system arise from intrinsic losses (i.e., absorption) in the resonator modes and from atomic spontaneous emission into free space.…”

Creation of a squeezed photon distribution using artificial atoms with broken inversion symmetry

“…The precision of these measurements is fundamentally limited due to shot noise caused by the quantized nature of light and the photon statistics of the radiation source. To circumvent this limitation, squeezed light has been theoretically proposed [1][2][3][4][5][6] and successfully applied in physical [7][8][9] and biological experiments [10,11].…”