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Chinese Journal of Lasers

Experimental Techniques for Quantum Wavepacket Interferometer

Chen Lei

Published Jan 1, 2001• 0 citations
OpenAlex

Abstract

The quantum wavepacket interference in rare earth ions is observed with dual-channel correlation spectroscopic technique using a femtosecond laser. The measured dephasing time of Eu 3+ ions in Y 2O 3∶Eu 3+ at room temperature is longer than 3 picoseconds, and the quantum wavepacket interference is recorded in the free-induction decay process of Eu 3+ ions. Some systematic errors in the experiments are discussed and the solutions are suggested. Experimental skills are reported.

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Chinese Physics Letters•Feb 1, 2000•6 citations

Hong-Ou-Mandel interference with absorption and dispersion from rare earth ions

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The coherent interactions between photons and rare earth ion ensembles are crucial for quantum storage and quantum information processing. Hong-Ou-Mandel (HOM) interference, a well-known quantum interference phenomenon, has been widely used in precision measurement applications. However, there have been no reports to date on observing coherent interactions between light and ionic ensembles using HOM interferometry. In this study, we experimentally generated entangled photons from two 10-mm-long type-0 phase-matched PPKTP crystals. Then we constructed a HOM interferometer and achieved a HOM dip with a visibility of 82.4% and a width of 152.5 ± 0.2 fs. Finally, we inserted a N d3+ : Y V O4 (rare earth ion) crystal into the optical path and successfully observed the splitting of the HOM dip. This experiment may provide valuable insights into light-matter interactions and could be beneficial for quantum storage applications.

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Quantum interference in the presence of a resonant medium

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Interaction of light with media often occurs with a femtosecond response time. Its measurement by conventional techniques requires the use of femtosecond lasers and sophisticated time-gated optical detection. Here we demonstrate that by exploiting quantum interference of entangled photons it is possible to measure the dephasing time of a resonant media on the femtosecond time scale (down to 100 fs) using accessible continuous wave laser and single-photon counting. We insert a sample in the Hong-Ou-Mandel interferometer and observe the modification of the two-photon interference pattern, which is driven by the coherent response of the medium, determined by the dephasing time. The dephasing time is then inferred from the observed pattern. This effect is distinctively different from the basic effect of spectral filtering, which was studied in earlier works. In addition to its ease of use, our technique does not require compensation of group velocity dispersion and does not induce photo-damage of the samples. Our technique will be useful for characterization of ultrafast phase relaxation processes in material science, chemistry, and biology.

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We theoretically and experimentally demonstrate the quantum coherent control of the resonance-mediated two-photon absorption in rare-earth ions by the phase-shaped femtosecond laser pulse. Our theoretical results show that the resonance-mediated two-photon absorption can be effectively controlled, but the control efficiency depends on the laser repetition rate in real experiment due to the long lifetime and the short decoherence time of the excited state, and the larger laser repetition rate yields the lower control efficiency. These theoretical results are experimentally confirmed in glass sample doped with Er3+ by utilizing the femtosecond lasers with low repetition rate of 1 kHz and high repetition rate of 80 MHz.

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Light-Matter Interaction and Quantum Computing in Rare-Earth-Ion-Doped Crystals

Adam Kinos

In this thesis, crystals of yttrium orthosilicate (Y2SiO5) that are randomly doped with another rare-earth element, such as praseodymium (Pr), europium (Eu), or cerium (Ce), are investigated with lasers locked to ultra-stable cavities using the Pound-Drever-Hall locking technique. Many of these rare-earth elements have long-lived 4f-4f transitions, hundreds of microseconds to a few milliseconds, with even longer ground hyperfine lifetimes of up to several days. The coherence properties are, to the best of the author's knowledge, the longest achieved for any material, currently with a record of six hours for the nuclear spin states of Eu3+:Y2SiO5 measured at cryogenic temperatures. Furthermore, due to natural trapping and differences in the local environments, each dopant ion experiences a slightly different crystal field, and thus an inhomogeneity in the 4f-4f transition exists between all ions in a crystal. Since the homogeneous linewidth is in the order of kHz or below, whereas the inhomogeneous profile can be several GHz wide, these materials have dense storing capabilities.This thesis explores how light interacts with such rare-earth-ion-doped crystals; how the absorption and light polarization varies during propagation; how spectral features in the inhomogeneous absorption profile can be tailored to create narrowband spectral filters; how the speed of light is slowed down significantly in such narrow transmission windows; and how that can be used to either frequency shift incoming light, control its group velocity, or temporally compress pulses. It also uses rare-earth-ions to research quantum computing, the field of using quantum mechanical effects such as superpositions and entanglements to outperform classical computers on certain specific problems. This is done by examining how two-color pulses can be used to rapidly induce coherence from an initially mixed state; how qubit-qubit interactions can be performed experimentally using ensemble qubits, which opens the door to two-qubit experiments such as the CNOT-gate and entanglements; how a scalable quantum computer might be constructed using a single ion qubit approach with a dedicated readout ion and buffer ion(s) to improve readout fidelity; and how cerium is investigated as a candidate for such a dedicated readout ion.

•Feb 5, 2018•0 citations
The quantum wavepacket interference in rare earth ions is observed with dual-channel correlation spectroscopic technique using a femtosecond laser. The measured dephasing time of Eu 3+ ions in Y 2O 3∶Eu 3+ at room temperature is longer than 3 picoseconds, and the quantum wavepacket interference is recorded in the free-induction decay process of Eu 3+ ions. Some systematic errors in the experiments are discussed and the solutions are suggested. Experimental skills are reported.
The coherent interactions between photons and rare earth ion ensembles are crucial for quantum storage and quantum information processing. Hong-Ou-Mandel (HOM) interference, a well-known quantum interference phenomenon, has been widely used in precision measurement applications. However, there have been no reports to date on observing coherent interactions between light and ionic ensembles using HOM interferometry. In this study, we experimentally generated entangled photons from two 10-mm-long type-0 phase-matched PPKTP crystals. Then we constructed a HOM interferometer and achieved a HOM dip with a visibility of 82.4% and a width of 152.5 ± 0.2 fs. Finally, we inserted a N d3+ : Y V O4 (rare earth ion) crystal into the optical path and successfully observed the splitting of the HOM dip. This experiment may provide valuable insights into light-matter interactions and could be beneficial for quantum storage applications.
Interaction of light with media often occurs with a femtosecond response time. Its measurement by conventional techniques requires the use of femtosecond lasers and sophisticated time-gated optical detection. Here we demonstrate that by exploiting quantum interference of entangled photons it is possible to measure the dephasing time of a resonant media on the femtosecond time scale (down to 100 fs) using accessible continuous wave laser and single-photon counting. We insert a sample in the Hong-Ou-Mandel interferometer and observe the modification of the two-photon interference pattern, which is driven by the coherent response of the medium, determined by the dephasing time. The dephasing time is then inferred from the observed pattern. This effect is distinctively different from the basic effect of spectral filtering, which was studied in earlier works. In addition to its ease of use, our technique does not require compensation of group velocity dispersion and does not induce photo-damage of the samples. Our technique will be useful for characterization of ultrafast phase relaxation processes in material science, chemistry, and biology.
We theoretically and experimentally demonstrate the quantum coherent control of the resonance-mediated two-photon absorption in rare-earth ions by the phase-shaped femtosecond laser pulse. Our theoretical results show that the resonance-mediated two-photon absorption can be effectively controlled, but the control efficiency depends on the laser repetition rate in real experiment due to the long lifetime and the short decoherence time of the excited state, and the larger laser repetition rate yields the lower control efficiency. These theoretical results are experimentally confirmed in glass sample doped with Er3+ by utilizing the femtosecond lasers with low repetition rate of 1 kHz and high repetition rate of 80 MHz.
Matter-wave interferometers are sensitive probes of low energy physics and have been used for precise tests of gravity and quantum mechanics. These applications would benefit from interfering particles of higher mass, but observing the interference of a large particle is challenging due to the need to control its initial state and to avoid decoherence. Here we propose to demonstrate matter-wave interference of a microparticle with an embedded rare-earth ion. Optical transitions of the rare-earth ion will impart momentum to the microparticle's center of mass. The use of a time-symmetric interferometer geometry and a rare-earth ion state with angular momentum J=1/2J = 1/2J=1/2 will eliminate sensitivity to the initial conditions of the microparticle. We show that the rates of all relevant external decoherence mechanisms either decrease or remain constant as the microparticle mass is increased, allowing decoherence to be avoided by using sufficiently large particles. An apparatus at moderate vacuum levels will support microparticle interferometry with up to 10310^3103 photons per beam splitter and millisecond coherence time. This demonstration will establish microparticle interferometry as a new platform for quantum sensing, improving searches for minimal modifications of quantum mechanics by up to three orders of magnitude in the near term and laying the foundation for future gravitational tests.
In this thesis, crystals of yttrium orthosilicate (Y2SiO5) that are randomly doped with another rare-earth element, such as praseodymium (Pr), europium (Eu), or cerium (Ce), are investigated with lasers locked to ultra-stable cavities using the Pound-Drever-Hall locking technique. Many of these rare-earth elements have long-lived 4f-4f transitions, hundreds of microseconds to a few milliseconds, with even longer ground hyperfine lifetimes of up to several days. The coherence properties are, to the best of the author's knowledge, the longest achieved for any material, currently with a record of six hours for the nuclear spin states of Eu3+:Y2SiO5 measured at cryogenic temperatures. Furthermore, due to natural trapping and differences in the local environments, each dopant ion experiences a slightly different crystal field, and thus an inhomogeneity in the 4f-4f transition exists between all ions in a crystal. Since the homogeneous linewidth is in the order of kHz or below, whereas the inhomogeneous profile can be several GHz wide, these materials have dense storing capabilities.This thesis explores how light interacts with such rare-earth-ion-doped crystals; how the absorption and light polarization varies during propagation; how spectral features in the inhomogeneous absorption profile can be tailored to create narrowband spectral filters; how the speed of light is slowed down significantly in such narrow transmission windows; and how that can be used to either frequency shift incoming light, control its group velocity, or temporally compress pulses. It also uses rare-earth-ions to research quantum computing, the field of using quantum mechanical effects such as superpositions and entanglements to outperform classical computers on certain specific problems. This is done by examining how two-color pulses can be used to rapidly induce coherence from an initially mixed state; how qubit-qubit interactions can be performed experimentally using ensemble qubits, which opens the door to two-qubit experiments such as the CNOT-gate and entanglements; how a scalable quantum computer might be constructed using a single ion qubit approach with a dedicated readout ion and buffer ion(s) to improve readout fidelity; and how cerium is investigated as a candidate for such a dedicated readout ion.