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- Hyunchul Nha, H J Carmichael
- Physical review letters
- 2004

We propose a test of nonlocality for continuous variables using a two-mode squeezed state as the source of nonlocal correlations and a measurement scheme based on conditional homodyne detection. Both the Clauser-Horne-Shimony-Holt and the Clauser-Horne inequality are constructed from the conditional homodyne data and found to be violated for a squeezing… (More)

- Hyunchul Nha, M Suhail Zubairy
- Physical review letters
- 2008

In this Letter, we show that the fulfillment of uncertainty relations is a sufficient criterion for a quantum-mechanically permissible state. We specifically construct two pseudospin observables for an arbitrary nonpositive Hermitian matrix whose uncertainty relation is violated. This method enables us to systematically derive separability conditions for… (More)

- Hyunchul Nha, H J Carmichael
- Physical review letters
- 2004

The degree of entanglement in an open quantum system varies according to how information in the environment is read. A measure of this contextual entanglement is introduced based on quantum trajectory unravelings of the open system dynamics. It is used to characterize the entanglement in a driven quantum system of dimension 2 x infinity where the… (More)

- Hyunchul Nha, Su-Yong Lee, Se-Wan Ji, M S Kim
- Physical review letters
- 2012

We present a formalism to derive entanglement criteria beyond the Gaussian regime that can be readily tested by only homodyne detection. The measured observable is the Einstein-Podolsky-Rosen (EPR) correlation. Its arbitrary functional form enables us to detect non-Gaussian entanglement even when an entanglement test based on second-order moments fails. We… (More)

- Jaehak Lee, M S Kim, Hyunchul Nha
- Physical review letters
- 2010

We address the degradation of continuous variable (CV) entanglement in a noisy channel focusing on the set of photon-number entangled states. We exploit several separability criteria and compare the resulting separation times with the value of non-Gaussianity at any time, thus showing that in the low-temperature regime: (i) non-Gaussianity is a bound for… (More)

- Jiyong Park, Junhua Zhang, +5 authors Hyunchul Nha
- Physical review letters
- 2015

We theoretically propose and experimentally demonstrate a nonclassicality test of a single-mode field in phase space, which has an analogy with the nonlocality test proposed by Banaszek and Wódkiewicz [Phys. Rev. Lett. 82, 2009 (1999)]. Our approach to deriving the classical bound draws on the fact that the Wigner function of a coherent state is a product… (More)

- Se-Wan Ji, Jaehak Lee, Jiyong Park, Hyunchul Nha
- Scientific reports
- 2016

Quantum steering-a strong correlation to be verified even when one party or its measuring device is fully untrusted-not only provides a profound insight into quantum physics but also offers a crucial basis for practical applications. For continuous-variable (CV) systems, Gaussian states among others have been extensively studied, however, mostly confined to… (More)

- Su-Yong Lee, Chang-Woo Lee, Jaehak Lee, Hyunchul Nha
- Scientific reports
- 2016

We study the sensitivity of phase estimation using a generic class of path-symmetric entangled states |φ〉|0〉 + |0〉|φ〉, where an arbitrary state |φ〉 occupies one of two modes in quantum superposition. With this generalization, we identify the fundamental limit of phase estimation under energy constraint that is characterized by the photon statistics of the… (More)

- Qingqing Sun, Hyunchul Nha, Suhail Zubairy
- 2009

We demonstrate how to efficiently derive a broad class of inequalities for entanglement detection in multimode continuous variable systems. The separability conditions are established from partial transposition PT in combination with several distinct necessary conditions for a quantum physical state, which include previously established inequalities as… (More)

Abstract. Conditional homodyne detection of quadrature squeezing is compared with standard nonconditional detection. Whereas the latter identifies nonclassicality in a quantitative way, as a reduction of the noise power below the shot noise level, conditional detection makes a qualitative distinction between vacuum state squeezing and squeezed classical… (More)