Quantum limits in interferometric measurements

Quantum noise limits the sensitivity of interferometric measurements. It is generally admitted that it leads to an ultimate sensitivity, the ``standard quantum limit''. Using a semi-classical analysis of quantum noise, we show that a judicious use of squeezed states allows one in principle to push the sensitivity beyond this limit. This general method could be applied to large scale interferometers designed for gravitational wave detection.Comment: 4 page

Entangled and disentangled evolution for a single atom in a driven cavity

For an atom in an externally driven cavity, we show that special initial states lead to near-disentangled atom-field evolution, and superpositions of these can lead to near maximally-entangled states. Somewhat counterintutively, we find that (moderate) spontaneous emission in this system actually leads to a transient increase in entanglement beyond the steady-state value. We also show that a particular field correlation function could be used, in an experimental setting, to track the time evolution of this entanglement

Constraints for quantum logic arising from conservation laws and field fluctuations

We explore the connections between the constraints on the precision of quantum logical operations that arise from a conservation law, and those arising from quantum field fluctuations. We show that the conservation-law based constraints apply in a number of situations of experimental interest, such as Raman excitations, and atoms in free space interacting with the multimode vacuum. We also show that for these systems, and for states with a sufficiently large photon number, the conservation-law based constraint represents an ultimate limit closely related to the fluctuations in the quantum field phase.Comment: To appear in J. Opt. B: Quantum Semiclass. Opt., special issue on quantum contro

Pembangunan Aplikasi Perhitungan Honor Dan Pengukuran Kinerja Asisten Praktikum Berbasis SaaS

Bagi suatu perguruan tinggi, kegiatan praktikum sangat penting untuk mendukung pembelajaran di kelas. Beberapa masalah yang muncul dalam pengelolaan kegiatan praktikum seperti keterlambatan pengumpulan berita acara praktikum (BAP) sehingga memperlambat perhitungan, pembayaran dan pelaporan honor asprak. Dibutuhkan waktu sekitar dua minggu untuk rekapitulasi dan validasi ratusan lembar BAP yang telah terkumpul setiap bulannya. Dibutuhkan pengolahan data lebih lanjut untuk menilai kinerja asprak berdasarkan data BAP. Untuk mengatasi permasalahan di atas maka dibangun aplikasi perhitungan honor dan kinerja asprak. Aplikasi ini digunakan untuk mengelola data BAP, perhitungan dan pelaporan honor, perhitungan nilai transkrip aktivitas kemahasiswaan (TAK) dan pencetakan sertifikat asprak. Keterbatasan SDM atau biaya menyebabkan tidak semua perguruan tinggi dapat langsung membuat aplikasi yang dibutuhkan. Oleh karena itu aplikasi ini dibangun berbasis Software as A Service (SaaS). Aplikasi ini dikembangkan dengan metode analisis perancangan terstruktur dengan model waterfall. Pengumpulan data kebutuhan aplikasi dilakukan dengan survey ke fakultas-fakultas di Universitas Telkom. Hasilnya dianalisis dan dikembangkan menjadi rancangan aplikasi. Aplikasi diimplementasikan pada pemrograman PHP. Pengujian dilakukan dengan metode black box testing. Hasilnya berupa aplikasi SaaS untuk perhitungan honor dan pengukuran kinerja asisten praktikum. Perguruan tinggi pengguna aplikasi SaaS ini dapat melakukan kostumisasi terhadap fitur yang ada sesuai dengan kebutuhan

Can quantum chaos enhance stability of quantum computation?

We consider stability of a general quantum algorithm with respect to a fixed but unknown residual interaction between qubits, and show a surprising fact, namely that the average fidelity of quantum computation increases by decreasing average time correlation function of the perturbing operator in sequences of consecutive quantum gates. Our thinking is applied to the quantum Fourier transformation where an alternative 'less regular' quantum algorithm is devised which is qualitatively more robust against static random residual n-qubit interaction.Comment: 4 pages, 5 eps figures (3 color

Dynamical localization simulated on a few qubits quantum computer

We show that a quantum computer operating with a small number of qubits can simulate the dynamical localization of classical chaos in a system described by the quantum sawtooth map model. The dynamics of the system is computed efficiently up to a time $t\geq \ell$, and then the localization length $\ell$ can be obtained with accuracy $\nu$ by means of order $1/\nu^2$ computer runs, followed by coarse grained projective measurements on the computational basis. We also show that in the presence of static imperfections a reliable computation of the localization length is possible without error correction up to an imperfection threshold which drops polynomially with the number of qubits.Comment: 8 pages, 8 figure

Computation using Noise-based Logic: Efficient String Verification over a Slow Communication Channel

Utilizing the hyperspace of noise-based logic, we show two string verification methods with low communication complexity. One of them is based on continuum noise-based logic. The other one utilizes noise-based logic with random telegraph signals where a mathematical analysis of the error probability is also given. The last operation can also be interpreted as computing universal hash functions with noise-based logic and using them for string comparison. To find out with 10^-25 error probability that two strings with arbitrary length are different (this value is similar to the error probability of an idealistic gate in today's computer) Alice and Bob need to compare only 83 bits of the noise-based hyperspace.Comment: Accepted for publication in European Journal of Physics B (November 10, 2010