期刊
NPJ QUANTUM INFORMATION
卷 6, 期 1, 页码 -出版社
NATURE PORTFOLIO
DOI: 10.1038/s41534-020-00321-x
关键词
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类别
资金
- NTU-IBM Q Hub [MOST 107-2627-E-002-001-MY3]
- Graduate Student Study Abroad Program [MOST 107-2917-I-006-002]
- Ministry of Science and Technology, Taiwan [108-2811-M-006-536, MOST 107-2628-M-006-002-MY3, MOST 107-2811-M-006-017, MOST 107-2627-E-006-001]
- JST PRESTO [JPMJPR18GC]
- National Center for Theoretical Sciences [MOST 107-2628-M-006-002-MY3, MOST 107-2811-M-006-017, MOST 107-2627-E-006-001]
- Army Research Office [W911NF-19-1-0081]
- EPSRC [EP/P034012/1]
- NTT Research
- Army Research Office (ARO) [W911NF-18-1-0358]
- Japan Science and Technology Agency (JST) (Q-LEAP)
- Japan Science and Technology Agency (JST) (CREST) [JPMJCR1676]
- Japan Society for the Promotion of Science (JSPS) (KAKENHI) [JP20H00134]
- Japan Society for the Promotion of Science (JSPS) (CREST) [JPMJCR1676]
- Japan Society for the Promotion of Science (JSPS) (JSPS-RFBR) [JPJSBP120194828]
- Asian Office of Aerospace Research and Development (AOARD)
- Foundational Questions Institute Fund (FQXi) [FQXi-IAF19-06]
- EPSRC [EP/P034012/1] Funding Source: UKRI
The Leggett-Garg inequality attempts to classify experimental outcomes as arising from one of two possible classes of physical theories: those described by macrorealism (which obey our intuition about how the macroscopic classical world behaves) and those that are not (e.g., quantum theory). The development of cloud-based quantum computing devices enables us to explore the limits of macrorealism. In particular, here we take advantage of the properties of the programmable nature of the IBM quantum experience to observe the violation of the Leggett-Garg inequality (in the form of a 'quantum witness') as a function of the number of constituent systems (qubits), while simultaneously maximizing the 'disconnectivity', a potential measure of macroscopicity, between constituents. Our results show that two- and four-qubit 'cat states' (which have large disconnectivity) are seen to violate the inequality, and hence can be classified as non-macrorealistic. In contrast, a six-qubit cat state does not violate the 'quantum witness' beyond a so-called clumsy invasive-measurement bound, and thus is compatible with 'clumsy macrorealism'. As a comparison, we also consider un-entangled product states with n=2, 3, 4 and 6 qubits, in which the disconnectivity is low.
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