50 research outputs found
Strong measurements give a better direct measurement of the quantum wave function
Weak measurements have thus far been considered instrumental in the so-called
direct measurement of the quantum wavefunction [Nature (London) 474, 188
(2011)]. Here we show that direct measurement of the wavefunction can be
obtained by using measurements of arbitrary strength. In particular, in the
case of strong measurements, i.e. those in which the coupling between the
system and the measuring apparatus is maximum, we compared the precision and
the accuracy of the two methods, by showing that strong measurements outperform
weak measurements in both for arbitrary quantum states in most cases. We also
give the exact expression of the difference between the reconstructed and
original wavefunctions obtained by the weak measurement approach: this will
allow to define the range of applicability of such method.Comment: Updated version, 5 pages + Supplementary Informatio
Wide energy range trigger and development of new electronics for ICARUS LAr-TPC
The ICARUS-T600 detector, with its 470 tons of active mass, is the largest Liquid Argon TPC (LAr-TPC) ever built, and is now currently operating in the LNGS underground laboratory, detecting cosmic rays events after 3 years of data taking with the CERN Neutrinos to Gran Sasso beam. Its excellent calorimetric resolution and topol- ogy reconstruction capabilities permit a wide physics program, which goes from nucleon decay to the study of the oscillation of the neutrinos from the CNGS beam. The events collected differ both for energy deposition (ranging from tens of MeV to tens of GeV) and for topology. To get a fully-efficient detection of the interesting events it is thus necessary to exploit all available sources in the trigger system: the scintillation light, the charge signal on wires and timing information (for beam-related events).
For the 2010-2013 data taking a primary trigger, based on the signal from the photomultipliers placed inside the detector, has been set up. To enhance the efficiency of this setup for CNGS neutrino events, a particular effort has been addressed to the development of a time synchronization with the spill extraction, which allowed to reduce the trigger threshold in coincidence with the neutrino arrival time. To check the PMT efficiency for the CNGS events, an alternative minimum biasing trigger has been also developed, which is based on the time synchronization as well as on the analysis of the charge deposition on the TPC wires. A full efficiency and a rejection of more than 103 have been reached with this trigger.
To further increase the PMT trigger efficiency on non beam related events, an hit finding algorithm has been implemented in a hardware device, and is now taking data in steady condition. First results of this recently installed system, have shown an increase of the overall trigger efficiency on the sub-GeV region, which is of particular interest in view of the study of nucleon decay as well as on the low energy tail of the atmospheric neutrons.
Finally ICARUS solved the anomaly reported by the OPERA collaborations on the superluminar neutrino velocity, by performing a high precision measurement of the neutrino time of flight from CERN to LNGS, resulting in perfectly agreement, within the experimental resolution, with the light velocity
Experimental Satellite Quantum Communications
Quantum Communications on planetary scale require complementary channels
including ground and satellite links. The former have progressed up to
commercial stage using fiber-cables, while for satellite links, the absence of
terminals in orbit has impaired theirs development. However, the demonstration
of the feasibility of such links is crucial for designing space payloads and to
eventually enable the realization of protocols such as quantum-key-distribution
(QKD) and quantum teleportation along satellite-to-ground or intersatellite
links. We demonstrated the faithful transmission of qubits from space to ground
by exploiting satellite corner cube retroreflectors acting as transmitter in
orbit, obtaining a low error rate suitable for QKD. We also propose a two-way
QKD protocol exploiting modulated retroreflectors that necessitates a minimal
payload on satellite, thus facilitating the expansion of Space Quantum
Communications
Experimental single photon exchange along a space link of 7000 km
Extending the single photon transmission distance is a basic requirement for
the implementation of quantum communication on a global scale. In this work we
report the single photon exchange from a medium Earth orbit satellite (MEO) at
more than 7000 km of slanted distance to the ground station at the Matera Laser
Ranging Observatory. The single photon transmitter was realized by exploiting
the corner cube retro-reflectors mounted on the LAGEOS-2 satellite. Long
duration of data collection is possible with such altitude, up to 43 minutes in
a single passage. The mean number of photons per pulse ({\mu}sat) has been
limited to 1 for 200 seconds, resulting in an average detection rate of 3.0 cps
and a signal to noise ratio of 1.5. The feasibility of single photon exchange
from MEO satellites paves the way to tests of Quantum Mechanics in moving
frames and to global Quantum Information.Comment: 5 pages, updated versio
Fast and simple qubit-based synchronization for quantum key distribution
We propose Qubit4Sync, a synchronization method for Quantum Key Distribution
(QKD) setups, based on the same qubits exchanged during the protocol and
without requiring additional hardware other than the one necessary to prepare
and measure the quantum states. Our approach introduces a new cross-correlation
algorithm achieving the lowest computational complexity, to our knowledge, for
high channel losses. We tested the robustness of our scheme in a real QKD
implementation
Interference at the Single Photon Level Along Satellite-Ground Channels
Quantum interference arising from superposition of states is a striking
evidence of the validity of Quantum Mechanics, confirmed in many experiments
and also exploited in applications. However, as for any scientific theory,
Quantum Mechanics is valid within the limits in which it has been
experimentally verified. In order to extend such limits, it is necessary to
observe quantum interference in unexplored conditions such as moving terminals
at large distance in Space. Here we experimentally demonstrate single photon
interference at a ground station due to the coherent superposition of two
temporal modes reflected by a rapidly moving satellite thousand kilometers
away. The relative speed of the satellite induces a varying modulation in the
interference pattern. The measurement of the satellite distance in real time by
laser ranging allowed us to precisely predict the instantaneous value of the
interference phase. We then observed the interference patterns with visibility
up to with three different satellites and with path length up to 5000
km. Our results attest the viability of photon temporal modes for fundamental
tests of Physics and Quantum Communications in Space.Comment: Version accepted for publication in Phys. Rev. Let
Direct Reconstruction of the Quantum Density Matrix by Strong Measurements
New techniques based on weak measurements have recently been introduced to
the field of quantum state reconstruction. Some of them allow the direct
measurement of each matrix element of an unknown density operator and need only
different operations, compared to linearly independent projectors
in the case of standard quantum state tomography, for the reconstruction of an
arbitrary mixed state. However, due to the weakness of these couplings, these
protocols are approximated and prone to large statistical errors. We propose a
method which is similar to the weak measurement protocols but works regardless
of the coupling strength: our protocol is not approximated and thus improves
the accuracy and precision of the results with respect to weak measurement
schemes. We experimentally apply it to the polarization state of single photons
and compare the results to those of preexisting methods for different values of
the coupling strength. Our results show that our method outperforms previous
proposals in terms of accuracy and statistical errors.Comment: RevTex, 6 page
Towards Quantum Communication from Global Navigation Satellite System
Satellite-based quantum communication is an invaluable resource for the
realization of a quantum network at the global scale. In this regard, the use
of satellites well beyond the low Earth orbits gives the advantage of long
communication time with a ground station. However, high-orbit satellites pose a
great technological challenge due to the high diffraction losses of the optical
channel, and the experimental investigation of such quantum channels is still
lacking. Here, we report on the first experimental exchange of single photons
from Global Navigation Satellite System at a slant distance of 20000
kilometers, by exploiting the retroreflector array mounted on GLONASS
satellites. We also observed the predicted temporal spread of the reflected
pulses due to the geometrical shape of array. Finally, we estimated the
requirements needed for an active source on a satellite, aiming towards quantum
communication from GNSS with state-of-the-art technology.Comment: Revte
Extending Wheeler's delayed-choice experiment to Space
Gedankenexperiments have consistently played a major role in the development
of quantum theory. A paradigmatic example is Wheeler's delayed-choice
experiment, a wave-particle duality test that cannot be fully understood using
only classical concepts. Here, we implement Wheeler's idea along a
satellite-ground interferometer which extends for thousands of kilometers in
Space. We exploit temporal and polarization degrees of freedom of photons
reflected by a fast moving satellite equipped with retro-reflecting mirrors. We
observed the complementary wave-like or particle-like behaviors at the ground
station by choosing the measurement apparatus while the photons are propagating
from the satellite to the ground. Our results confirm quantum mechanical
predictions, demonstrating the need of the dual wave-particle interpretation,
at this unprecedented scale. Our work paves the way for novel applications of
quantum mechanics in Space links involving multiple photon degrees of freedom.Comment: 4 figure