We study the problem of quantum temporal imaging in the case where the time lens is implemented by a sum frequency generation nonlinear process. We consider the general case where the time lens is characterized by a finite aperture and a not-perfect phase-matching in a regime close to 100% conversion efficiency. In particular we tackle this problem in term of the eigenmodes of the entire transformation of the field in the temporal imaging system. We show that in the case of modeling the phase-matching function by a double Gaussian the eigenmodes are given by chirped Gauss-Hermite functions. The effective number of involved eigenmodes is estimated as the ratio of the temporal aperture of the lens to the walk-off time of the signal and the idler waves in the nonlinear crystal. Our theoretical treatment allows us to identify the criteria for designing imaging schemes with close to unity efficiencies
Temporal imaging is a technique enabling manipulation of temporal optical signals in a manner similar to manipulation of optical images in spatial domain. The quantum description of temporal imaging is relevant in the context of long range quantum communication. Indeed this technology relies on the efficiency of quantum repeaters for which the temporal mode matching between the quantum emitters, the communication network and the quantum memories is critical. In this work we address the problem of temporal imaging of a temporally broadband squeezed light generated by a traveling-wave optical parametric amplifier. We consider a single-lens temporal imaging system formed by two dispersive elements and a parametric temporal lens, based on a non- linear process such as sum-frequency generation or four-wave mixing. We derive a unitary transformation of the field operators performed by this kind of time lens and evaluate the squeezing spectrum at the output of the single-lens imaging system. When the efficiency factor of the temporal lens is smaller than unity, the vacuum fluctuations deteriorate squeezing at its output. For efficiency close to unity, when certain imaging conditions are satisfied, the squeezing spectrum at the output of the imaging system will be the same as that at the output of the OPA in terms of the scaled frequency ΩI = MΩ which corresponds to the scaled time tI = t/M . The magnification factor M gives the possibility of matching the coherence time of the broadband squeezed light to the response time of the photodetector.
Quantum superpositions of coherent states are produced both in microwave and optical domains, and are considered realizations of the famous “Schroedinger cat” state. The recent progress shows an increase in the number of components and the number of modes involved. Our work gives a theoretical treatment of multicomponent two-mode Schroedinger cat states. We consider a class of single-mode states, which are superpositions of N coherent states lying on a circle in the phase space. In this class we consider an orthonormal basis created by rotationally-invariant circular states (RICS). A two-mode extension of this basis is created by splitting a single-mode RICS on a balanced beam-splitter. After performing a symmetric (Loewdin) orthogonalization of the sets of coherent states in both modes we obtain the Schmidt decomposition of the two-mode state, and therefore an analytic expression for its entanglement. We show that the states obtained by splitting a RICS are generalizations of Bell states of two qubits to the case of N -level systems encoded into superpositions of coherent states on the circle, and we propose for them the name of generalized quasi-Bell states. We show that an exact probabilistic teleportation of arbitrary superposition of coherent states on the circle is possible with such a state used as shared resource.
We calculate the Schmidt number for a two-dimensional model of the nonfactorable spatiotemporal wave-function
of biphotons produced in type-I spontaneous parametric down-conversion with degenerate and collinear phase-
matching taking into consideration a major part of the broad spectral and angular bandwidth of the down-
converted light. We derive an analytical expression for the Schmidt number as a function of the filter bandwidth
in the limit of spectrally narrow pump.
The quantum key distribution protocol ΒΒ84 combined with the repetition protocol for error correction are analyzed
from the viewpoint of security against individual eavesdropping empowered by quantum memory. We show that a mere
knowledge of the error correction protocol changes the optimal attack and provides the eavesdropper with additional
information about the generated key.
An effective and robust method for generating random bits from random time intervals between quantum jumps of
optical field is proposed and experimentally tested with spontaneous switchings in a bistable vertical-cavity surface-emitting
laser. This algorithm allows one to avoid the problem of biasing in the output bit stream as well as to obtain low
correlation between generated bits. A comprehensive comparative statistical analysis of different methods of extraction
of random bits from experimentally measured time intervals between spontaneous polarization switchings in a bistable
vertical-cavity surface-emitting laser shows the advantage of the proposed method.
We give a definition of asyimnetric universal entangling machine, entangling a system in an unknown state to
a specially prepared ancilla. We describe explicitly such a machine for a d-level quantmn system and prove its