39 research outputs found
Quantum Stopwatch: How To Store Time in a Quantum Memory
Quantum mechanics imposes a fundamental tradeoff between the accuracy of time
measurements and the size of the systems used as clocks. When the measurements
of different time intervals are combined, the errors due to the finite clock
size accumulate, resulting in an overall inaccuracy that grows with the
complexity of the setup. Here we introduce a method that in principle eludes
the accumulation of errors by coherently transferring information from a
quantum clock to a quantum memory of the smallest possible size. Our method
could be used to measure the total duration of a sequence of events with
enhanced accuracy, and to reduce the amount of quantum communication needed to
stabilize clocks in a quantum network.Comment: 10 + 5 pages, 3 figure
Probabilistic metrology or how some measurement outcomes render ultra-precise estimates
We show on theoretical grounds that, even in the presence of noise,
probabilistic measurement strategies (which have a certain probability of
failure or abstention) can provide, upon a heralded successful outcome,
estimates with a precision that exceeds the deterministic bounds for the
average precision. This establishes a new ultimate bound on the phase
estimation precision of particular measurement outcomes (or sequence of
outcomes). For probe systems subject to local dephasing, we quantify such
precision limit as a function of the probability of failure that can be
tolerated. Our results show that the possibility of abstaining can set back the
detrimental effects of noise.Comment: Improved version of arXiv:1407.6910 with an extended introduction
where we clarify our approach to metrology, and probabilistic metrology in
particular. Changed titl
Quantum Communication, Sensing and Measurement in Space
The main theme of the conclusions drawn for classical communication systems
operating at optical or higher frequencies is that there is a wellâunderstood
performance gain in photon efficiency (bits/photon) and spectral efficiency
(bits/s/Hz) by pursuing coherentâstate transmitters (classical ideal laser light)
coupled with novel quantum receiver systems operating near the Holevo limit (e.g.,
joint detection receivers). However, recent research indicates that these receivers
will require nonlinear and nonclassical optical processes and components at the
receiver. Consequently, the implementation complexity of Holevoâcapacityapproaching
receivers is not yet fully ascertained. Nonetheless, because the
potential gain is significant (e.g., the projected photon efficiency and data rate of
MIT Lincoln Laboratory's Lunar Lasercom Demonstration (LLCD) could be achieved
with a factorâofâ20 reduction in the modulation bandwidth requirement), focused
research activities on groundâreceiver architectures that approach the Holevo limit
in spaceâcommunication links would be beneficial.
The potential gains resulting from quantumâenhanced sensing systems in space
applications have not been laid out as concretely as some of the other areas
addressed in our study. In particular, while the study period has produced several
interesting highârisk and highâpayoff avenues of research, more detailed seedlinglevel
investigations are required to fully delineate the potential return relative to
the stateâofâtheâart. Two prominent examples are (1) improvements to pointing,
acquisition and tracking systems (e.g., for optical communication systems) by way
of quantum measurements, and (2) possible weakâvalued measurement techniques
to attain highâaccuracy sensing systems for in situ or remoteâsensing instruments.
While these concepts are technically sound and have very promising benchâtop
demonstrations in a lab environment, they are not mature enough to realistically
evaluate their performance in a spaceâbased application. Therefore, it is
recommended that future work follow small focused efforts towards incorporating
practical constraints imposed by a space environment.
The space platform has been well recognized as a nearly ideal environment for some
of the most precise tests of fundamental physics, and the ensuing potential of
scientific advances enabled by quantum technologies is evident in our report. For
example, an exciting concept that has emerged for gravityâwave detection is that the
intermediate frequency band spanning 0.01 to 10 Hzâwhich is inaccessible from
the groundâcould be accessed at unprecedented sensitivity with a spaceâbased
interferometer that uses shorter arms relative to stateâofâtheâart to keep the
diffraction losses low, and employs frequencyâdependent squeezed light to surpass
the standard quantum limit sensitivity. This offers the potential to open up a new
window into the universe, revealing the behavior of compact astrophysical objects
and pulsars. As another set of examples, research accomplishments in the atomic
and optics fields in recent years have ushered in a number of novel clocks and
sensors that can achieve unprecedented measurement precisions. These emerging
technologies promise new possibilities in fundamental physics, examples of which
are tests of relativistic gravity theory, universality of free fall, frameâdragging
precession, the gravitational inverseâsquare law at micron scale, and new ways of gravitational wave detection with atomic inertial sensors. While the relevant
technologies and their discovery potentials have been well demonstrated on the
ground, there exists a large gap to spaceâbased systems. To bridge this gap and to
advance fundamentalâphysics exploration in space, focused investments that further
mature promising technologies, such as spaceâbased atomic clocks and quantum
sensors based on atomâwave interferometers, are recommended.
Bringing a group of experts from diverse technical backgrounds together in a
productive interactive environment spurred some unanticipated innovative
concepts. One promising concept is the possibility of utilizing a spaceâbased
interferometer as a frequency reference for terrestrial precision measurements.
Spaceâbased gravitational wave detectors depend on extraordinarily low noise in
the separation between spacecraft, resulting in an ultraâstable frequency reference
that is several orders of magnitude better than the state of the art of frequency
references using terrestrial technology. The next steps in developing this promising
new concept are simulations and measurement of atmospheric effects that may limit
performance due to nonâreciprocal phase fluctuations.
In summary, this report covers a broad spectrum of possible new opportunities in
space science, as well as enhancements in the performance of communication and
sensing technologies, based on observing, manipulating and exploiting the
quantumâmechanical nature of our universe. In our study we identified a range of
exciting new opportunities to capture the revolutionary capabilities resulting from
quantum enhancements. We believe that pursuing these opportunities has the
potential to positively impact the NASA mission in both the near term and in the
long term. In this report we lay out the research and development paths that we
believe are necessary to realize these opportunities and capitalize on the gains
quantum technologies can offer
Precision bounds in noisy quantum metrology
In an idealistic setting, quantum metrology protocols allow to sense physical
parameters with mean squared error that scales as with the number of
particles involved---substantially surpassing the -scaling characteristic
to classical statistics. A natural question arises, whether such an impressive
enhancement persists when one takes into account the decoherence effects that
are unavoidable in any real-life implementation. In this thesis, we resolve a
major part of this issue by describing general techniques that allow to
quantify the attainable precision in metrological schemes in the presence of
uncorrelated noise. We show that the abstract geometrical structure of a
quantum channel describing the noisy evolution of a single particle dictates
then critical bounds on the ultimate quantum enhancement. Our results prove
that an infinitesimal amount of noise is enough to restrict the precision to
scale classically in the asymptotic limit, and thus constrain the maximal
improvement to a constant factor. Although for low numbers of particles the
decoherence may be ignored, for large the presence of noise heavily alters
the form of both optimal states and measurements attaining the ultimate
resolution. However, the established bounds are then typically achievable with
use of techniques natural to current experiments. In this work, we thoroughly
introduce the necessary concepts and mathematical tools lying behind
metrological tasks, including both frequentist and Bayesian estimation theory
frameworks. We provide examples of applications of the methods presented to
typical qubit noise models, yet we also discuss in detail the phase estimation
tasks in Mach-Zehnder interferometry both in the classical and quantum
setting---with particular emphasis given to photonic losses while analysing the
impact of decoherence.Comment: PhD Thesis (defended 22.09.2014). 138 pages, 6 chapters (+10
appendices), 20 figures, 6 tables. Final version containing modifications
suggested by the referees: Dariusz Chruscinski and Andrzej Grudka.
Incorporates and extends the material of arXiv:1006.0734, arXiv:1201.3940,
arXiv:1303.7271 and arXiv:1405.770
Experimental multiparameter quantum metrology in adaptive regime
Relevant metrological scenarios involve the simultaneous estimation of
multiple parameters. The fundamental ingredient to achieve quantum-enhanced
performances is based on the use of appropriately tailored quantum probes.
However, reaching the ultimate resolution allowed by physical laws requires non
trivial estimation strategies both from a theoretical and a practical point of
view. A crucial tool for this purpose is the application of adaptive learning
techniques. Indeed, adaptive strategies provide a flexible approach to obtain
optimal parameter-independent performances, and optimize convergence to the
fundamental bounds with limited amount of resources. Here, we combine on the
same platform quantum-enhanced multiparameter estimation attaining the
corresponding quantum limit and adaptive techniques. We demonstrate the
simultaneous estimation of three optical phases in a programmable integrated
photonic circuit, in the limited resource regime. The obtained results show the
possibility of successfully combining different fundamental methodologies
towards transition to quantum sensors applications
Advances in photonic quantum sensing
Quantum sensing has become a mature and broad field. It is generally related
with the idea of using quantum resources to boost the performance of a number
of practical tasks, including the radar-like detection of faint objects, the
readout of information from optical memories or fragile physical systems, and
the optical resolution of extremely close point-like sources. Here we first
focus on the basic tools behind quantum sensing, discussing the most recent and
general formulations for the problems of quantum parameter estimation and
hypothesis testing. With this basic background in our hands, we then review
emerging applications of quantum sensing in the photonic regime both from a
theoretical and experimental point of view. Besides the state-of-the-art, we
also discuss open problems and potential next steps.Comment: Review in press on Nature Photonics. This is a preliminary version to
be updated after publication. Both manuscript and reference list will be
expande
Quantum Communication, Sensing and Measurement in Space
The main theme of the conclusions drawn for classical communication systems
operating at optical or higher frequencies is that there is a wellâunderstood
performance gain in photon efficiency (bits/photon) and spectral efficiency
(bits/s/Hz) by pursuing coherentâstate transmitters (classical ideal laser light)
coupled with novel quantum receiver systems operating near the Holevo limit (e.g.,
joint detection receivers). However, recent research indicates that these receivers
will require nonlinear and nonclassical optical processes and components at the
receiver. Consequently, the implementation complexity of Holevoâcapacityapproaching
receivers is not yet fully ascertained. Nonetheless, because the
potential gain is significant (e.g., the projected photon efficiency and data rate of
MIT Lincoln Laboratory's Lunar Lasercom Demonstration (LLCD) could be achieved
with a factorâofâ20 reduction in the modulation bandwidth requirement), focused
research activities on groundâreceiver architectures that approach the Holevo limit
in spaceâcommunication links would be beneficial.
The potential gains resulting from quantumâenhanced sensing systems in space
applications have not been laid out as concretely as some of the other areas
addressed in our study. In particular, while the study period has produced several
interesting highârisk and highâpayoff avenues of research, more detailed seedlinglevel
investigations are required to fully delineate the potential return relative to
the stateâofâtheâart. Two prominent examples are (1) improvements to pointing,
acquisition and tracking systems (e.g., for optical communication systems) by way
of quantum measurements, and (2) possible weakâvalued measurement techniques
to attain highâaccuracy sensing systems for in situ or remoteâsensing instruments.
While these concepts are technically sound and have very promising benchâtop
demonstrations in a lab environment, they are not mature enough to realistically
evaluate their performance in a spaceâbased application. Therefore, it is
recommended that future work follow small focused efforts towards incorporating
practical constraints imposed by a space environment.
The space platform has been well recognized as a nearly ideal environment for some
of the most precise tests of fundamental physics, and the ensuing potential of
scientific advances enabled by quantum technologies is evident in our report. For
example, an exciting concept that has emerged for gravityâwave detection is that the
intermediate frequency band spanning 0.01 to 10 Hzâwhich is inaccessible from
the groundâcould be accessed at unprecedented sensitivity with a spaceâbased
interferometer that uses shorter arms relative to stateâofâtheâart to keep the
diffraction losses low, and employs frequencyâdependent squeezed light to surpass
the standard quantum limit sensitivity. This offers the potential to open up a new
window into the universe, revealing the behavior of compact astrophysical objects
and pulsars. As another set of examples, research accomplishments in the atomic
and optics fields in recent years have ushered in a number of novel clocks and
sensors that can achieve unprecedented measurement precisions. These emerging
technologies promise new possibilities in fundamental physics, examples of which
are tests of relativistic gravity theory, universality of free fall, frameâdragging
precession, the gravitational inverseâsquare law at micron scale, and new ways of gravitational wave detection with atomic inertial sensors. While the relevant
technologies and their discovery potentials have been well demonstrated on the
ground, there exists a large gap to spaceâbased systems. To bridge this gap and to
advance fundamentalâphysics exploration in space, focused investments that further
mature promising technologies, such as spaceâbased atomic clocks and quantum
sensors based on atomâwave interferometers, are recommended.
Bringing a group of experts from diverse technical backgrounds together in a
productive interactive environment spurred some unanticipated innovative
concepts. One promising concept is the possibility of utilizing a spaceâbased
interferometer as a frequency reference for terrestrial precision measurements.
Spaceâbased gravitational wave detectors depend on extraordinarily low noise in
the separation between spacecraft, resulting in an ultraâstable frequency reference
that is several orders of magnitude better than the state of the art of frequency
references using terrestrial technology. The next steps in developing this promising
new concept are simulations and measurement of atmospheric effects that may limit
performance due to nonâreciprocal phase fluctuations.
In summary, this report covers a broad spectrum of possible new opportunities in
space science, as well as enhancements in the performance of communication and
sensing technologies, based on observing, manipulating and exploiting the
quantumâmechanical nature of our universe. In our study we identified a range of
exciting new opportunities to capture the revolutionary capabilities resulting from
quantum enhancements. We believe that pursuing these opportunities has the
potential to positively impact the NASA mission in both the near term and in the
long term. In this report we lay out the research and development paths that we
believe are necessary to realize these opportunities and capitalize on the gains
quantum technologies can offer
Photonic Quantum Metrology
Quantum Metrology is one of the most promising application of quantum
technologies. The aim of this research field is the estimation of unknown
parameters exploiting quantum resources, whose application can lead to enhanced
performances with respect to classical strategies. Several physical quantum
systems can be employed to develop quantum sensors, and photonic systems
represent ideal probes for a large number of metrological tasks. Here we review
the basic concepts behind quantum metrology and then focus on the application
of photonic technology for this task, with particular attention to phase
estimation. We describe the current state of the art in the field in terms of
platforms and quantum resources. Furthermore, we present the research area of
multiparameter quantum metrology, where multiple parameters have to be
estimated at the same time. We conclude by discussing the current experimental
and theoretical challenges, and the open questions towards implementation of
photonic quantum sensors with quantum-enhanced performances in the presence of
noise.Comment: 51 pages, 9 figures, 967 references. Comments and feedbacks are very
welcom
Fisher Information and entanglement of non-Gaussian spin states
In this thesis, we study a novel method to extract the Fisher information of quantum states from direct measurements without the need for state reconstruction. Our method characterizes the distinguishability of experimental probability distributions of the collective spin. The Fisher information is obtained via the observed rate of change of their statistical distance as a function of an experimental control parameter, which constitutes a phase transformation of the quantum state. The employed experimental system is a binary Bose-Einstein condensate of several hundred atoms. We use a combination of coherent collisional interaction and linear Rabi coupling of the two atomic states to generate collective non-classical spin states via quantum dynamics close to an unstable fixed point of the corresponding classical system. The fast redistribution of quantum uncertainty results in Gaussian spin-squeezed states for short evolution times which turn into non-Gaussian states on an experimentally feasible time scale. For the generated non-Gaussian states we observe a Fisher information larger than the number of atoms in the detected ensemble, which is a signature of particle entanglement, in a regime where no spin-squeezing is present. We confirm the implied resource for quantumenhanced measurements with the implementation of a model-free Bayesian protocol which obtains a sensitivity beyond the standard quantum limit in accordance with the extracted Fisher information