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Byoung S. Ham

Publications and source records attributed to Byoung S. Ham.

50 records · Page 3Linked to original sources
arXiv2020

The origin of correlation fringe in Franson-type experiments

Nonlocal correlation is the key concept in quantum information processing, where quantum entanglement provides such a nonclassical property. Since the first proposal of noninterfering interferometer-based two-photon intensity correlation by Franson (Phys. Rev. Lett. 62, 2205 (1989)), the particle nature of photons has been intensively studied for nonlocal correlation using Mach-Zehnder interferometers (MZIs). Here, the role of MZIs is investigated with respect to the origin of nonlocal correlation in Franson-type experiments, where the wave nature of photons plays a critical role. Under the coincidence-provided quantum superposition between independent MZIs, we prove that nonlocal correlation can be created from non-entangled photons through the MZIs.

quant-ph↗
arXiv2019

Unconditionally secured classical cryptography using quantum superposition and unitary transformation

Over decades quantum cryptography has been intensively studied for unconditionally secured data transmission in a quantum regime. Due to the quantum loopholes caused by imperfect single photon detectors and/or lossy quantum channels, however, the quantum cryptography is practically inefficient and even vulnerable to eavesdropping. Here, a method of unconditionally secured key distribution potentially compatible with current fiber-optic communications networks is proposed in a classical regime for high-speed optical backbone networks. The unconditional security is due to the quantum superposition-caused measurement indistinguishability of a paired transmission channel and its unitary transformation resulting in deterministic randomness corresponding to the no-cloning theorem in a quantum regime.

quant-ph↗
arXiv2018

Addressable optical key distribution for unconditionally secured cryptography using phase-controlled quantum superposition

Based on the detection loophole-free photon key distribution (PKD) compatible with classical optical systems, an optical key distribution (OKD) protocol is presented for unconditionally secured cryptography in fiber-optic communications networks using addressable continuous phase basis, where each communication channel is composed of paired transmission lines. The unconditional security in OKD lies in quantum superposition between the paired lines of each channel. The continuous phase basis in OKD can be applied for one-time-pad optical cryptography in networks, whose network address capacity is dependent upon the robustness of OKD to channel noises.

quant-ph↗
arXiv2018

Wavelength convertible quantum memory satisfying ultralong photon storage and near perfect retrieval efficiency

Quantum coherence control is presented for wavelength convertible quantum memory in a double-lambda-type solid ensemble whose spin states are inhomogeneously broadened. Unlike typical atomic media whose spin decay is homogeneous, a spin inhomogeneously broadened solid ensemble requires a counter-intuitive access in the quantum coherence control to avoid spontaneous emission-caused quantum noises. Such quantum coherence control in a solid ensemble results in a near perfect retrieval efficiency and is applicable to ultralong photon storage up to the spin phase relaxation time. Here, the basic physics of the counter-intuitive quantum coherence control is presented not only for two-photon (Raman) coherent transients, but also for a detailed coherence transfer mechanism resulting in frequency up-/down-conversion. This work sheds light on potential applications of quantum optical memories satisfying noise free, near perfect, ultralong, and multimode photon storage, where quantum repeaters, scalable entangled qubits, and magnetometry would be imminent beneficiaries.

quant-ph↗
arXiv2016

Atom phase controlled noise-free photon echoes

Rephasing in photon echoes is a fundamental mechanism of retrieving optical information stored in a collective ensemble of atoms or ions. With an extremely weak quantum optical data, population inversion by the rephasing process is inevitable resulting in serious quantum noise. Here, an inversion-free rephasing method in photon echoes is presented by using deshelving-based atom phase control. The present method makes photon echoes directly applicable to quantum memories with benefits of extended photon storage time and nearly perfect retrieval efficiency. In this revised version only the rephasing pulse propagation direction is corrected to make a silent echo of E1 in Fig. 1.

quant-ph↗
arXiv2012

Dynamic Control of Magnetically Trapped Indirect Excitons by Using External Magnetic Bias

We demonstrate an on demand spatial control of excitonic magnetic lattices for the potential applications of excitonic-based quantum optical devices. A two dimensional magnetic lattice of indirect excitons can form a transition to one dimensional lattice configuration under the influence of external magnetic bias fields. The transition is identified by measuring the spatial distribution of two dimensional photoluminance for several values of the external magnetic bias fields. The number of the trapped excitons is found to increase between sites along a perpendicular direction exhibiting two to one dimensional lattice transition. This work may apply for various controllable quantum simulations, such as superfluid-Mott-insulators, in quantum optical devices.

cond-mat.quant-gas↗
arXiv2012

Observations of indirect exciton trapping in one- and two-dimensional magnetic lattices

A simple method to create and control magnetic potentials onto coupled quantum wells is demonstrated for indirect-exciton magnetic confinement. Localized inhomogeneous magnetic potentials with periodically distributed local minima and maxima, known as magnetic lattices, are projected into the plane of the coupled quantum wells and used for the spatially distributed two-dimensional indirect-exciton trapping, in which case localized indirect-excitons are observed. The indirect-exciton trapping mechanism is examined by controlling external magnetic field bias resulting in a shift of the localized excitonic lattice.

cond-mat.mes-hall↗
arXiv2011

Inversion-free, noiseless Raman echoes

Using double optical Raman rephasing, an inversion-free resonant Raman echo is studied in an inhomogeneously broadened spin ensemble of a solid medium, where the Raman optical field-excited spin coherence has a frozen propagation vector. Unlike photon echoes whose quantum memory application is strictly limited due to πrephasing pulse-induced population inversion causing quantum noises, the optical Raman field-excited spin echo is inherently silent owing to the frozen propagation vector. Thus, the doubly rephased Raman echo can be directly applied for quantum interface in a population inversion-free environment.

quant-ph↗
arXiv2010

On-demand control of photon echoes far exceeding the spin coherence constraint via coherence swapping between optical and spin transitions

Using on-demand coherence conversion via optical locking in conventional stimulated (three-pulse) photon echoes, ultralong, ultraefficient photon storage has been observed in a rare-earth Pr3+ doped Y2SiO5, where storage time is several orders of magnitude longer and retrieval efficiency is enhanced by fifty times. Compared with the same method applied to two-pulse photon echoes for a rephasing halt, use of spectral grating in the stimulated photon echoes offers a phase-independent coherence conversion between optical and spin states. Eventually an ultralong spin population decay-dependent photon storage protocol is achieved by applying optical locking to a spectral grating in conventional stimulated photon echoes. The present breakthrough in both photon storage time and retrieval efficiency opens a door to long-distance quantum communications utilizing quantum repeaters.

quant-ph↗
arXiv2010

Ultralong Efficient Photon Storage Using Optical Locking

For the last decade quantum memories have been intensively studied for potential applications to quantum information and communications using atomic and ionic ensembles. With the importance of a multimode storage capability in quantum memories, on-demand control of reversible inhomogeneous broadening of an optical medium has been broadly investigated recently. However, the photon storage time in these researches is still too short to apply for long-distance quantum communications. In this paper, we demonstrate new physics of spin population decay dependent ultralong photon storage method, where spin population decay time is several orders of magnitude longer than the conventional constraint of spin phase decay time.

quant-ph↗
arXiv2010

Analysis of Optical Deshelving in Photon Echo-based Quantum Memories

Storage time extension in photon echoes using optical deshelving via a robust spin state has been investigated for absorption-dependent optical leakage, where an incomplete population transfer, even by a πoptical pulse obviates the phase recovery condition of the deshelving. We analyze an optical depth-dependent echo leakage mechanism in the storage time extended photon echoes for the usage of optical deshelving to photon echo-based quantum memories.

quant-ph↗
arXiv2009

Towards Bose-Einstein condensation of excitons in an asymmetric multi-quantum state magnetic lattice

An asymmetric multi-quantum state magnetic lattice is proposed to host excitons formed in a quantum degenerate gas of ultracold fermionic atoms to simulate Bose-Einstein condensation (BEC) of excitons. A Quasi-two dimensional degenerate gas of excitons can be collected in the in-plane asymmetric magnetic bands created at the surface of the proposed magnetic lattice, where the ultracold fermions simulate separately direct and indirect confined electronhole pairs (spin up fermions-spin down fermions) rising to the statistically degenerate Bose gas and eventually through controlled tunnelling to BEC of excitons. The confinement of the coupled magnetic quantum well (CMQWs) system may significantly improve the condition for long lived exciton BEC. The exciton BEC, formed in CMQWs can be regarded as a suitable host for the multi-qubits (multipartite) systems to be used in quantum information processors.

quant-ph↗
arXiv2008

Ultralong quantum optical storage using reversible inhomogeneous spin ensembles with an optical locking method

A novel method of multi-bit quantum optical data storage is presented, where the storage time can be lengthened far beyond the spin phase-decay time in a reversible spin inhomogeneous system excited by consecutive resonant Raman optical data pulses. The ultralong storage time is obtained by an optical population locking mechanism of modified rephasing process. This gives potentials to quantum repeaters utilizing quantum memories for long distance quantum communications, in which ultralong storage time plays a major role.

quant-ph↗