Experimental temporal quantum steering

Abstract

Temporal steering is a form of temporal correlation between the initial and final state of a quantum system. It is a temporal analogue of the famous Einstein-Podolsky-Rosen (spatial) steering. We demonstrate, by measuring the photon polarization, that temporal steering allows two parties to verify if they have been interacting with the same particle, even if they have no information about what happened with the particle in between the measurements. This is the first experimental study of temporal steering. We also performed experimental tests, based on the violation of temporal steering inequalities, of the security of two quantum key distribution protocols against individual attacks. Thus, these results can lead to applications for secure quantum communications and quantum engineering.Einstein-Podolsky-Rosen (EPR) steering refers to strong nonclassical nonlocal bipartite correlations. It was first described by Schrödinger 1 as a generalization of the EPR paradox 2 . The recent celebration of the 80 years of steering and the EPR paradox 3 showed that our understanding of this phenomenon is now much deeper, but still very limited. Steering differs from quantum entanglement 4 and Bell nonlocality 5-7 , as not every entangled state manifests steering and not every state that manifests steering violates Bell's inequality 8 . In other words, steerable states are a subset of entangled states and a superset of Bell nonlocal states. Analogously to Bell nonlocality, steering can be detected independently of other nonclassical correlations by simple inequalities [8][9][10] that can include as little as two measurements with two outcomes for Alice and a set of four possible states for Bob 9 . Such inequalities were tested in several experiments [10][11][12][13][14][15][16][17] , including a recent loophole-free experiment 18 . Steering can be interpreted as a correlation between two systems (measuring devices), where only one of them is trusted. This property shows an operational meaning of steering and indicates its potential applications in quantum cryptography and quantum communication, e.g., for entanglement distribution 8,19 . Steering-based protocols can provide secure communications even when only one party trusts its devices. Such protocols are easier to implement than completely-device-independent protocols 20 , but are more secure than standard protocols requiring mutual trust between the communicating parties.Temporal steering 21 (TS), analogously to EPR steering, is observed when Alice can steer Bob's state into one of two orthogonal states by properly choosing her measured observable. Despite this similarity, the implications of these temporal and spatial phenomena are fundamentally different. To detect TS 21 , Alice and Bob perform consecutive measurements (using a random sequence of mutually-unbiased bases known only to them) on the same system to test temporal correlations between its initial and final states. Breaking the temporal steering inequality, given in ref. 21, implies that no unauthorised party ca...

Einstein-Podolsky-Rosen steering: Its geometric quantification and witness

“…Thus, EPR steering is a form of quantum correlation, which can be classified between entanglement and Bell nonlocality, in the following meaning: it certifies the entanglement between two systems assuming trusted measurements only on one of these [4]. Eighty years of research on EPR steering has resulted in many experimental demonstrations [8][9][10][11][12][13][14][15][16][17][18][19][20][21] and various applications [22][23][24][25][26], which include multipartite quantum steering [27][28][29][30][31], the correspondence with measurement incompatibility [32][33][34][35][36], one-way steering [20,[37][38][39], one sided device-independent processing in quantum key distribution [40], continuous-variable EPR steering [29,[41][42][43], as well as temporal [44][45][46][47][48][49] and spatio-temporal steering…”

Quantum steering and entanglement in three-mode triangle Bose–Hubbard system

“…As it was quite recently shown, the steering effect, besides its commonly discussed form which is related to the EPR nonlocality [2], has its temporal [3][4][5] and spatiotemporal forms [6]. It should be noted that quantum B W. Leoński w.leonski@if.uz.zgora.pl 1 Quantum Optics and Engineering Division, Faculty of Physics and Astronomy, University of Zielona Góra, Prof. Z. Szafrana 4a, 65-516 Zielona Góra, Poland 2 Institute of Physics, Czȩstochowa University of Technology, Armii Krajowej 19, Czȩstochowa, Poland steering is weaker than Bell-type correlations but stronger than quantum entanglement.…”

Measuring distances in Hilbert space by many-particle interference

“…This measure due to being Euclidean has intuitive geometric properties that can be utilized in depicting relations between quantum states (see, e.g., Ref. [17]) Trace distance of two mixed states is related to the fidelity by the following inequalities…”