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Recovering coherence from decoherence : a method of quantum state reconstruction
| Content Provider | Semantic Scholar |
|---|---|
| Author | Roversi, José Antônio Dutra, Suzana Maria Velloso Vidiella-Barranco, Antonio |
| Copyright Year | 1999 |
| Abstract | The reconstruction of quantum states is a central topic in quantum optics and related fields [1,2]. During the past years, several techniques have been developed, for instance, the direct sampling of the density matrix of a signal mode in multiport optical homodyne tomography [3], tomographic reconstruction by unbalanced homodyning [4], cascaded homodyning [5] and reconstruction via photocounting [6]. There are also proposals of measurement of the electromagnetic field inside a cavity [7] as well as the vibrational state of an ion in a trap [8]. The full reconstruction of nonclassical field states [9] as well as of (motional) states of an ion [10] have been already experimentally accomplished. The quantum state reconstruction is normally achieved through a finite set of either field homodyne measurements, or selective measurement of atomic states [7] in the case of cavities. This makes possible to construct a quasidistribution (such as the the Wigner function) which constitutes an alternative representation of the quantum state of the field. Nevertheless, in real experiments, the presence of noise and dissipation has normally destructive effects. In fact, as it has been already pointed out, the reconstruction schemes themselves also indicate loss of coherence in quantum systems [10]. regarding this subject, a scheme for compensation of losses in quantum-state measurements has been already proposed [11], and the relation between losses and s-parameterized quasiprobability distributions has been already pointed out in [12]. The scheme on loss compensation in [11] applies to photodetector losses, and consists essentially of a mathematical inversion formula expressing the initial density matrix in terms of the decayed one. Our scheme, as discussed in [13], involves a physical process that actually enables us to store information about all the quantum coherences of the initial state in the diagonal elements (photon distribuition) of the density matrix of a transformed state. By storing this information in the diagonal elements, it becomes much more robust under dissipation, allowing us to recover the Wigner function of the initial field state in a time scale of the order of the energy decay time that is, of course, much longer than the extremely fast decoherence time scale that is normally associated with the dissipation of quantum coherences. We consider a single mode high-Q cavity where we suppose that a (nonclassical) field state ρ̂(0) is previously prepared. The first step of our method consists in driving the generated quantum state by a coherent pulse. The reconstruction of the field state may be accomplished after turning-off the driving field, i.e., at a time in which the cavity field has already suffered decay. We use the fact that by displacing the initial state (even while it is decaying) we make its quantum coherences robust enough to allow its experimental determination, at a later time, despite dissipation. We then show that the evolution of the cavity field is such that it directly yields the Wigner function of the initial nonclassical field simply by measuring the photon number distribution of the displaced field. For that we make direct use of the series representation of quasiprobability distributions [14]. A numerical simulation of our method is presented, and we take into account the action of dissipation while driving the initial field. This manuscript is organized as follows: in Sec. II we discuss, taking into account losses, the process of displacement of the initial field. In Sec. III we show how to reconstruct the initial cavity field after allowing the displaced field to |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://cds.cern.ch/record/396418/files/9908034.pdf |
| Language | English |
| Access Restriction | Open |
| Subject Keyword | Body cavities Coherence (physics) Computer simulation Density matrix Dental caries Displacement mapping Electromagnetic Fields Experiment Fall time Fock state Hearing Loss, High-Frequency Ions Iontophoresis Manuscripts Mathematics Mental Suffering Optics Photodetector Device Component Photons Physical Phenomenon or Property Quantum decoherence Quantum state Quantum system Sampling (signal processing) Sampling - Surgical action Tomographic reconstruction Unbalanced circuit Wigner quasiprobability distribution |
| Content Type | Text |
| Resource Type | Article |
