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Testing sequential quantum measurements: how can maximal knowledge be extracted?

Nagali E, Felicetti S, de Assis PL, D'Ambrosio V, Filip R, Sciarrino F - Sci Rep (2012)

Bottom Line: In this framework partial measurements can be carried out in order to extract only a portion of the information encoded in a quantum system, at the cost of inducing a limited amount of disturbance.Here we analyze experimentally the dynamics of sequential partial measurements carried out on a quantum system, focusing on the trade-off between the maximal information extractable and the disturbance.In particular we implement two sequential measurements observing that, by exploiting an adaptive strategy, is possible to find an optimal trade-off between the two quantities.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Fisica, Sapienza Università di Roma, Roma 00185, Italy.

ABSTRACT
The extraction of information from a quantum system unavoidably implies a modification of the measured system itself. In this framework partial measurements can be carried out in order to extract only a portion of the information encoded in a quantum system, at the cost of inducing a limited amount of disturbance. Here we analyze experimentally the dynamics of sequential partial measurements carried out on a quantum system, focusing on the trade-off between the maximal information extractable and the disturbance. In particular we implement two sequential measurements observing that, by exploiting an adaptive strategy, is possible to find an optimal trade-off between the two quantities.

Show MeSH
(a) Experimental setup adopted for the sequential measurement strategy for N = 2 measurement processes. The entangled state has been generated via spontaneous parametric down conversion. (b) Scheme of the measurement kit MKi: the kit is based on a Sagnac interferometer which allows to separately manipulate the horizontal and vertical polarizations adopting two half-waveplates (HWP) oriented at angles θa and θb, related by a shift of π/4 for the optimal configuration.
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f2: (a) Experimental setup adopted for the sequential measurement strategy for N = 2 measurement processes. The entangled state has been generated via spontaneous parametric down conversion. (b) Scheme of the measurement kit MKi: the kit is based on a Sagnac interferometer which allows to separately manipulate the horizontal and vertical polarizations adopting two half-waveplates (HWP) oriented at angles θa and θb, related by a shift of π/4 for the optimal configuration.

Mentions: The former relations have been experimentally implemented encoding the initial singlet state in the polarization of two photons A and B, , where (H, V) are linear horizontal and vertical polarization, respectively. The experimental setup is reported in Fig. 2 and we provide all details in the Methods section. The meter qubit M has been encoded in a different degree of freedom of the photon B, the linear momentum. In this way the extracted information corresponds to the correlations between the polarization of the photon A and the path of the photon B. When all the information is extracted, and thus the strength of the coupling is maximum, the correlation is perfect.


Testing sequential quantum measurements: how can maximal knowledge be extracted?

Nagali E, Felicetti S, de Assis PL, D'Ambrosio V, Filip R, Sciarrino F - Sci Rep (2012)

(a) Experimental setup adopted for the sequential measurement strategy for N = 2 measurement processes. The entangled state has been generated via spontaneous parametric down conversion. (b) Scheme of the measurement kit MKi: the kit is based on a Sagnac interferometer which allows to separately manipulate the horizontal and vertical polarizations adopting two half-waveplates (HWP) oriented at angles θa and θb, related by a shift of π/4 for the optimal configuration.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3379168&req=5

f2: (a) Experimental setup adopted for the sequential measurement strategy for N = 2 measurement processes. The entangled state has been generated via spontaneous parametric down conversion. (b) Scheme of the measurement kit MKi: the kit is based on a Sagnac interferometer which allows to separately manipulate the horizontal and vertical polarizations adopting two half-waveplates (HWP) oriented at angles θa and θb, related by a shift of π/4 for the optimal configuration.
Mentions: The former relations have been experimentally implemented encoding the initial singlet state in the polarization of two photons A and B, , where (H, V) are linear horizontal and vertical polarization, respectively. The experimental setup is reported in Fig. 2 and we provide all details in the Methods section. The meter qubit M has been encoded in a different degree of freedom of the photon B, the linear momentum. In this way the extracted information corresponds to the correlations between the polarization of the photon A and the path of the photon B. When all the information is extracted, and thus the strength of the coupling is maximum, the correlation is perfect.

Bottom Line: In this framework partial measurements can be carried out in order to extract only a portion of the information encoded in a quantum system, at the cost of inducing a limited amount of disturbance.Here we analyze experimentally the dynamics of sequential partial measurements carried out on a quantum system, focusing on the trade-off between the maximal information extractable and the disturbance.In particular we implement two sequential measurements observing that, by exploiting an adaptive strategy, is possible to find an optimal trade-off between the two quantities.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Fisica, Sapienza Università di Roma, Roma 00185, Italy.

ABSTRACT
The extraction of information from a quantum system unavoidably implies a modification of the measured system itself. In this framework partial measurements can be carried out in order to extract only a portion of the information encoded in a quantum system, at the cost of inducing a limited amount of disturbance. Here we analyze experimentally the dynamics of sequential partial measurements carried out on a quantum system, focusing on the trade-off between the maximal information extractable and the disturbance. In particular we implement two sequential measurements observing that, by exploiting an adaptive strategy, is possible to find an optimal trade-off between the two quantities.

Show MeSH