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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.

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(a) Concurrence C as function of the knowledge for N = 2 sequential measurements adopting an independent strategy (black squares) and the adaptive one (red circles). Black and red lines represent theoretical expectations (dashed lines for the ideal case, continuous ones rescaled by experimental imperfections) for the two approaches. (b) Numerical determination of adaptive basis depending on the measurement carried out in the first kit, expressed by the parameter ψ. (c) Experimental knowledge after N = 2 sequential adaptive measurements (red squares) compared to theoretical predictions for classical (black line), adaptive extraction (dashed-dot red line), and after N = 1 measurement (dashed blue line). (d) Experimental and theoretical behavior of concurrence as function of . Black squares and line refer to experimental N = 2 adaptive measurements and theoretical expectations, respectively. Analogously red dots and line refers to the experimental and theoretical results for the single quantum measurements.
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f4: (a) Concurrence C as function of the knowledge for N = 2 sequential measurements adopting an independent strategy (black squares) and the adaptive one (red circles). Black and red lines represent theoretical expectations (dashed lines for the ideal case, continuous ones rescaled by experimental imperfections) for the two approaches. (b) Numerical determination of adaptive basis depending on the measurement carried out in the first kit, expressed by the parameter ψ. (c) Experimental knowledge after N = 2 sequential adaptive measurements (red squares) compared to theoretical predictions for classical (black line), adaptive extraction (dashed-dot red line), and after N = 1 measurement (dashed blue line). (d) Experimental and theoretical behavior of concurrence as function of . Black squares and line refer to experimental N = 2 adaptive measurements and theoretical expectations, respectively. Analogously red dots and line refers to the experimental and theoretical results for the single quantum measurements.

Mentions: Firstly we consider two independent sequential measurements, that is, the second projection on the state is performed independently of the outcome of the first one. In this case the concurrence shows a dependence from the whole amount of knowledge extracted Ktot as , thus the maximum amount of information extractable from the system does not achieve the optimal trade-off with the decoherence induced. In Fig. 4-a we report the experimental behavior of the concurrence for this measurement strategy (black squares), where the total knowledge Ktot has been evaluated as in the single measurement procedure, combining outcomes 00 with 01 and 10 with 11. This strategy is related to the scenario in which a series of independent observers estimate an unknown state of a quantum system by performing consecutive measurements over the very same system35.


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) Concurrence C as function of the knowledge for N = 2 sequential measurements adopting an independent strategy (black squares) and the adaptive one (red circles). Black and red lines represent theoretical expectations (dashed lines for the ideal case, continuous ones rescaled by experimental imperfections) for the two approaches. (b) Numerical determination of adaptive basis depending on the measurement carried out in the first kit, expressed by the parameter ψ. (c) Experimental knowledge after N = 2 sequential adaptive measurements (red squares) compared to theoretical predictions for classical (black line), adaptive extraction (dashed-dot red line), and after N = 1 measurement (dashed blue line). (d) Experimental and theoretical behavior of concurrence as function of . Black squares and line refer to experimental N = 2 adaptive measurements and theoretical expectations, respectively. Analogously red dots and line refers to the experimental and theoretical results for the single quantum measurements.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: (a) Concurrence C as function of the knowledge for N = 2 sequential measurements adopting an independent strategy (black squares) and the adaptive one (red circles). Black and red lines represent theoretical expectations (dashed lines for the ideal case, continuous ones rescaled by experimental imperfections) for the two approaches. (b) Numerical determination of adaptive basis depending on the measurement carried out in the first kit, expressed by the parameter ψ. (c) Experimental knowledge after N = 2 sequential adaptive measurements (red squares) compared to theoretical predictions for classical (black line), adaptive extraction (dashed-dot red line), and after N = 1 measurement (dashed blue line). (d) Experimental and theoretical behavior of concurrence as function of . Black squares and line refer to experimental N = 2 adaptive measurements and theoretical expectations, respectively. Analogously red dots and line refers to the experimental and theoretical results for the single quantum measurements.
Mentions: Firstly we consider two independent sequential measurements, that is, the second projection on the state is performed independently of the outcome of the first one. In this case the concurrence shows a dependence from the whole amount of knowledge extracted Ktot as , thus the maximum amount of information extractable from the system does not achieve the optimal trade-off with the decoherence induced. In Fig. 4-a we report the experimental behavior of the concurrence for this measurement strategy (black squares), where the total knowledge Ktot has been evaluated as in the single measurement procedure, combining outcomes 00 with 01 and 10 with 11. This strategy is related to the scenario in which a series of independent observers estimate an unknown state of a quantum system by performing consecutive measurements over the very same system35.

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