2,353 research outputs found
Dynamics of Atom-Field Entanglement from Exact Solutions: Towards Strong Coupling and Non-Markovian Regimes
We examine the dynamics of bipartite entanglement between a two-level atom
and the electromagnetic field. We treat the Jaynes-Cummings model with a single
field mode and examine in detail the exact time evolution of entanglement,
including cases where the atomic state is initially mixed and the atomic
transition is detuned from resonance. We then explore the effects of other
nearby modes by calculating the exact time evolution of entanglement in more
complex systems with two, three, and five field modes. For these cases we can
obtain exact solutions which include the strong coupling regimes. Finally, we
consider the entanglement of a two-level atom with the infinite collection of
modes present in the intracavity field of a Fabre-Perot cavity. In contrast to
the usual treatment of atom-field interactions with a continuum of modes using
the Born-Markov approximation, our treatment in all cases describes the full
non-Markovian dynamics of the atomic subsystem. Only when an analytic
expression for the infinite mode case is desired do we need to make a weak
coupling assumption which at long times approximates Markovian dynamics.Comment: 12 pages, 5 figures; minor changes in grammar, wording, and
formatting. One unnecessary figure removed. Figure number revised (no longer
counts subfigures separately
Signal-to-pump back-action and self-oscillation in Double-Pump Josephson Parametric Amplifier
We present the theory of a Josephson parametric amplifier employing two pump
sources. Our calculations are based on Input-Output Theory, and can easily be
generalized to any coupled system involving parametric interactions. We analyze
the operation of the device, taking into account the feedback introduced by the
reaction of the signal and noise on the pump power, and in this framework,
compute the response functions of interest - signal and idler gains, internal
gain of the amplifier, and self-oscillation signal amplitude. To account for
this back-action between signal and pump, we adopt a mean-field approach and
self-consistently explore the boundary between amplification and
self-oscillation. The coincidence of bifurcation and self-oscillation
thresholds reveals that the origin of coherent emission of the amplifier lies
in the multi-wave mixing of the noise components. Incorporation of the
back-action leads the system to exhibit hysteresis, dependent on parameters
like temperature and detuning from resonance. Our analysis also shows that the
resonance condition itself changes in the presence of back-action and this can
be understood in terms of the change in plasma frequency of the junction. The
potential of the double pump amplifier for quantum-limited measurements and as
a squeezer is also discussed.Comment: 25 pages, 20 figures, three appendice
Analisis Biaya Produk Asphalt Mixing Plants (Amp) Di Pulau Timor
Pada proses produksi dan distribusihotmix, jarak antara sumber material dan jarak antara lokasi permintaan hotmix dengan AMP akanberpengaruh pada biaya transportasi dan kualitas campuran yang dikirim ke lokasi pekerjaan. Penelitian dilakukan pada lokasi-lokasi yang terdapat Asphalt Mixing Plant (AMP) di Pulau Timor.Metode penelitian yang dilakukan ialah dengan observasi langsung (survei) ke lokasi dan melakukan wawancara langsung.Teknik pengolahan dan analisis data menggunakan analisa perhitungan produktivitas alat dan perhitungan biaya.Berdasarkan hasil penelitian menunjukkan bahwa terdapat 12 unit AMP di Pulau Timor, dengan rincian 4 unit AMP di Kabupaten Kupang, 2 unit AMP di Kabupaten Timor Tengah Selatan (TTS), 2 unit AMP di Kabupaten Timor Tengah Utara (TTU), dan 4 unit AMP di Kabupaten Belu. Berdasarkan lokasi-lokasi tersebut, maka setelah dilakukan analisis perhitungan produktivitas kerja alat dan biaya maka diketahui bahwa produktivitas kerja alat sangat mempengaruhi waktu pekerjaan sebuah proyek jalan yang menggunakan hotmix, di mana dengan angka produktivitas kerja alat yang rendah akan mengakibatkan biaya yang digunakan untuk pekerjaan proyek jalan semakin besar, dan juga kualitas hotmix yang digunakan akan berkurang
Quantum Computing with Continuous-Variable Clusters
Continuous-variable cluster states offer a potentially promising method of
implementing a quantum computer. This paper extends and further refines
theoretical foundations and protocols for experimental implementation. We give
a cluster-state implementation of the cubic phase gate through photon
detection, which, together with homodyne detection, facilitates universal
quantum computation. In addition, we characterize the offline squeezed
resources required to generate an arbitrary graph state through passive linear
optics. Most significantly, we prove that there are universal states for which
the offline squeezing per mode does not increase with the size of the cluster.
Simple representations of continuous-variable graph states are introduced to
analyze graph state transformations under measurement and the existence of
universal continuous-variable resource states.Comment: 17 pages, 5 figure
Quantum limit of deterministic theories
We show that the quantum linear harmonic oscillator can be obtained in the
large limit of a classical deterministic system with SU(1,1) dynamical
symmetry. This is done in analogy with recent work by G.'t Hooft who
investigated a deterministic system based on SU(2). Among the advantages of our
model based on a non--compact group is the fact that the ground state energy is
uniquely fixed by the choice of the representation.Comment: 4 pages, 2 figures, minor corrections added. To appear in the
Proceedings of Waseda International Symposium on Fundamental Physics: "New
Perspectives in Quantum Physics", 12-15 November 2002, Waseda University,
Tokyo, Japa
Stochastic resonance in Gaussian quantum channels
We determine conditions for the presence of stochastic resonance in a lossy
bosonic channel with a nonlinear, threshold decoding. The stochastic resonance
effect occurs if and only if the detection threshold is outside of a "forbidden
interval". We show that it takes place in different settings: when transmitting
classical messages through a lossy bosonic channel, when transmitting over an
entanglement-assisted lossy bosonic channel, and when discriminating channels
with different loss parameters. Moreover, we consider a setting in which
stochastic resonance occurs in the transmission of a qubit over a lossy bosonic
channel with a particular encoding and decoding. In all cases, we assume the
addition of Gaussian noise to the signal and show that it does not matter who,
between sender and receiver, introduces such a noise. Remarkably, different
results are obtained when considering a setting for private communication. In
this case the symmetry between sender and receiver is broken and the "forbidden
interval" may vanish, leading to the occurrence of stochastic resonance effects
for any value of the detection threshold.Comment: 17 pages, 6 figures. Manuscript improved in many ways. New results on
private communication adde
Theory versus experiment for vacuum Rabi oscillations in lossy cavities
The 1996 Brune {\it et al.} experiment on vacuum Rabi oscillation is analyzed
by means of alternative models of atom-reservoir interaction. Agreement with
experimental Rabi oscillation data can be obtained if one defines jump
operators in the dressed-state basis, and takes into account thermal
fluctuations between dressed states belonging to the same manifold. Such
low-frequency transitions could be ignored in a closed cavity, but the cavity
employed in the experiment was open, which justifies our assumption. The cavity
quality factor corresponding to the data is , whereas
reported in the experiment was . The rate of decoherence arising
from opening of the cavity can be of the same order as an analogous correction
coming from finite time resolution (formally equivalent to
collisional decoherence). Peres-Horodecki separability criterion shows that the
rate at which the atom-field state approaches a separable state is controlled
by fluctuations between dressed states from the same manifold, and not by the
rate of transitions towards the ground state. In consequence, improving the
factor we do not improve the coherence properties of the cavity.Comment: typo in eq. (60) corrected; (older comments: 14 figures (1 added),
value of Q improved, a section on the Peres-Horodecki test of separability
added, various small improvements; v3 includes discussion of finite time
resolution, v4 includes microscopic derivation of the master equation
Scheme for generating entangled states of two field modes in a cavity
This paper considers a two-level atom interacting with two cavity modes with
equal frequencies. Applying a unitary transformation, the system reduces to the
analytically solvable Jaynes-Cummings model. For some particular field states,
coherent and squeezed states, the transformation between the two bare basis's,
related by the unitary transformation, becomes particularly simple. It is shown
how to generate, the highly non-classical, entangled coherent states of the two
modes, both in the zero and large detuning cases. An advantage with the zero
detuning case is that the preparation is deterministic and no atomic
measurement is needed. For the large detuning situation a measurement is
required, leaving the field in either of two orthogonal entangled coherent
states.Comment: Accepted in J. Mod. Opt.; 12 pages; Replaced with revised version.
Extended discussion of experimental realizations, earlier studies in the
field and on the frequency dependence in the adiabatic eliminatio
An efficient scheme for the deterministic maximal entanglement of N trapped ions
We propose a method for generating maximally entangled states of N two-level
trapped ions. The method is deterministic and independent of the number of ions
in the trap. It involves a controlled-NOT acting simultaneously on all the ions
through a dispersive interaction. We explore the potential application of our
scheme for high precision frequency standards.Comment: 4 pages, no figures, submitted to PRL, under review, Revised Version:
Incorporated referee comment
Decision and function problems based on boson sampling
Boson sampling is a mathematical problem that is strongly believed to be
intractable for classical computers, whereas passive linear interferometers can
produce samples efficiently. So far, the problem remains a computational
curiosity, and the possible usefulness of boson-sampling devices is mainly
limited to the proof of quantum supremacy. The purpose of this work is to
investigate whether boson sampling can be used as a resource of decision and
function problems that are computationally hard, and may thus have
cryptographic applications. After the definition of a rather general
theoretical framework for the design of such problems, we discuss their
solution by means of a brute-force numerical approach, as well as by means of
non-boson samplers. Moreover, we estimate the sample sizes required for their
solution by passive linear interferometers, and it is shown that they are
independent of the size of the Hilbert space.Comment: Close to the version published in PR
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