scholarly journals Experimentally reducing the quantum measurement back action in work distributions by a collective measurement

2019 ◽  
Vol 5 (3) ◽  
pp. eaav4944 ◽  
Author(s):  
Kang-Da Wu ◽  
Yuan Yuan ◽  
Guo-Yong Xiang ◽  
Chuan-Feng Li ◽  
Guang-Can Guo ◽  
...  
Keyword(s):  
Quantum Coherence ◽  
Single Photon ◽  
Projective Measurement ◽  
Interference Effects ◽  
Quantum Thermodynamics ◽  
Experimental Implementation ◽  
Back Action ◽  
Qubit States ◽  
Projective Measurements ◽  
Measurement Approach

In quantum thermodynamics, the standard approach to estimating work fluctuations in unitary processes is based on two projective measurements, one performed at the beginning of the process and one at the end. The first measurement destroys any initial coherence in the energy basis, thus preventing later interference effects. To decrease this back action, a scheme based on collective measurements has been proposed by Perarnau-Llobetet al. Here, we report its experimental implementation in an optical system. The experiment consists of a deterministic collective measurement on two identically prepared qubit states, encoded in the polarization and path degree of a single photon. The standard two-projective measurement approach is also experimentally realized for comparison. Our results show the potential of collective schemes to decrease the back action of projective measurements, and capture subtle effects arising from quantum coherence.

CLASSICAL AND QUANTUM CONTROL OF A SIMPLE QUANTUM SYSTEM

2007 ◽  
Vol 05 (06) ◽  
pp. 857-884 ◽  
Author(s):  
ZAIRONG XI ◽  
GUANGSHENG JIN
Keyword(s):  
Quantum Control ◽  
Projective Measurement ◽  
Initial State ◽  
Average Fidelity ◽  
Simple Quantum ◽  
Control Scheme ◽  
Back Action ◽  
Projective Measurements ◽  
Corrected Scheme ◽  
Optimum Measurement

A qubit which is prepared in one of two non-orthogonal states and subjected to bit-flipping noise is considered. The objective is to use measurement and feedback control to correct the state of the qubit. Three classical schemes using projective measurements, i.e. discrimination and re-preparation, do nothing and random preparation, have been discussed, and are not optimal with respect to a performance which is quantified by the average fidelity of the corrected state compared to the initial state. In addition, one quantum scheme using a non-projective measurement with an optimum measurement strength achieves the best trade-off between gaining information about the system and disturbing it through measurement back-action. The performance of a quantum control scheme outperforms the classical schemes. Furthermore, no universal corrected scheme is discussed.

scholarly journals Measurement of entropy and quantum coherence properties of two type-I entangled photonic qubits

2021 ◽  
Vol 53 (7) ◽  
Author(s):  
Ali Motazedifard ◽  
Seyed Ahmad Madani ◽  
N. S. Vayaghan
Keyword(s):  
Maximum Likelihood ◽  
Quantum Coherence ◽  
Single Photon ◽  
Bell Inequality ◽  
Bell State ◽  
Von Neumann Entropy ◽  
Entangled State ◽  
Type I ◽  
Variable Theory ◽  
High Brightness

AbstractUsing the type-I SPDC process in BBO nonlinear crystal, we generate a polarization-entangled state near to the maximally-entangled Bell-state with high-visibility (high-brightness) 98.50 ± 1.33% (87.71 ± 4.45%) for HV (DA) basis. We calculate the CHSH version of the Bell inequality, as a nonlocal realism test, and find a strong violation from the classical physics or any hidden variable theory, S = 2.71 ± 0.10. Via measuring the coincidence count rate in the SPDC process, we obtain the quantum efficiency of single-photon detectors around (25.5 ± 3.4)%, which is in good agreement to their manufacturer company. As expected, we verify the linear dependency of the CC rate vs. pump power of input CW-laser, which may yield to find the effective second-order susceptibility crystal. Using the theory of the measurement of qubits, includes a tomographic reconstruction of quantum states due to the linear set of 16 polarization-measurement, together with a maximum-likelihood-technique, which is based on the numerical optimization, we calculate the physical non-negative definite density matrices, which implies on the non-separability and entanglement of prepared state. By having the maximum likelihood density operator, we calculate precisely the entanglement measures such as Concurrence, entanglement of formation, tangle, logarithmic negativity, and different entanglement entropies such as linear entropy, Von-Neumann entropy, and Renyi 2-entropy. Finally, this high-brightness and low-rate entangled photons source can be used for short-range quantum measurements in the Lab.

scholarly journals Observing quantum coherence from photons scattered in free-space

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Shihan Sajeed ◽  
Thomas Jennewein
Keyword(s):  
Free Space ◽  
Quantum Coherence ◽  
Quantum Communication ◽  
Single Photon ◽  
Detector Array ◽  
Line Of Sight ◽  
Background Suppression ◽  
Single Photon Detector ◽  
High Background ◽  
Non Line Of Sight

AbstractQuantum channels in free-space, an essential prerequisite for fundamental tests of quantum mechanics and quantum technologies in open space, have so far been based on direct line-of-sight because the predominant approaches for photon-encoding, including polarization and spatial modes, are not compatible with randomly scattered photons. Here we demonstrate a novel approach to transfer and recover quantum coherence from scattered, non-line-of-sight photons analyzed in a multimode and imaging interferometer for time-bins, combined with photon detection based on a 8 × 8 single-photon-detector-array. The observed time-bin visibility for scattered photons remained at a high 95% over a wide scattering angle range of −450 to +450, while the individual pixels in the detector array resolve or track an image in its field of view of ca. 0.5°. Using our method, we demonstrate the viability of two novel applications. Firstly, using scattered photons as an indirect channel for quantum communication thereby enabling non-line-of-sight quantum communication with background suppression, and secondly, using the combined arrival time and quantum coherence to enhance the contrast of low-light imaging and laser ranging under high background light. We believe our method will instigate new lines for research and development on applying photon coherence from scattered signals to quantum sensing, imaging, and communication in free-space environments.

Bell States, Bell Operators, and Total Teleportation

2001 ◽  
Vol 56 (1-2) ◽  
pp. 128-132 ◽  
Author(s):  
E. DelRe ◽  
B. Crosignani ◽  
P. Di Porto
Keyword(s):  
Spin State ◽  
Single Photon ◽  
Bell States ◽  
Single Electron ◽  
Experimental Implementation ◽  
Physical Quantities

Abstract We identify the operators and the corresponding physical quantities whose measurement allows in principle to obtain total teleportation of the unknown spin state of a single electron. We introduce an analogous scheme for a single photon and discuss its experimental implementation.

Quantum coherence dynamics of three-qubit states in XY spin-chain environment

2018 ◽  
Vol 17 (11) ◽  
Author(s):  
Shaoying Yin ◽  
Jie Song ◽  
Xuexin Xu ◽  
Yujun Zhang ◽  
Shutian Liu
Keyword(s):  
Spin Chain ◽  
Quantum Coherence ◽  
Xy Spin Chain ◽  
Qubit States

scholarly journals Effects of Oceanic Turbulence on Orbital Angular Momenta of Optical Communications

2020 ◽  
Vol 8 (11) ◽  
pp. 869
Author(s):  
Shuang Zhai ◽  
Yun Zhu ◽  
Yixin Zhang ◽  
Zhengda Hu
Keyword(s):  
Dissipation Rate ◽  
Quantum Coherence ◽  
Single Photon ◽  
Beam Width ◽  
Communication Performance ◽  
Oceanic Turbulence ◽  
Angular Momenta ◽  
Optimal Beam ◽  
Lower Temperature ◽  
Inner Scale

The propagation properties of Laguerre-Gaussian beams in oceanic turbulence are investigated for both single-photon and biphoton cases. For single-photon communication, the channel capacity and trace distance are employed, both of which effectively reveal the communication performance via different viewpoints. For the biphoton case, we consider distributions of quantum resources including entanglement and quantum coherence. Turbulence conditions with a larger inner-scale and anisotropic factors, higher dissipation rate of kinetic energy, lower dissipation rate of the mean-squared temperature, and lower temperature-salinity contribution ratio combined with longer wavelength and an appropriate range of optimal beam width are beneficial to communication performances. Our results provide theoretical significance to improve the orbital-angular-momentum communication via oceanic turbulence.

Direct characterization of quantum dynamics with single-photon two-qubit states

2008 ◽  
Vol 77 (3) ◽  
Author(s):  
Wei-Tao Liu ◽  
Wei Wu ◽  
Ping-Xing Chen ◽  
Cheng-Zu Li ◽  
Jian-Min Yuan
Keyword(s):  
Quantum Dynamics ◽  
Single Photon ◽  
Qubit States
Sign in / Sign up

Export Citation Format

Share Document