New Journal of Physics -

Prof. Arun Kumar Pati and his student Som Kanjilal published a paper on Entanglement meter: estimation of entanglement with single copy in interferometer in New Journal of Physics. The other author of his paper is Vivek Pandey, Harish-Chandra Research Institute, Prayagraj.

Research work as explained by the authors:

Efficient certification and quantification of high dimensional entanglement of composite systems are challenging both theoretically as well as experimentally. Here, we demonstrate how to measure the linear entropy, negativity and the Schmidt number of bipartite systems from the visibility of Mach–Zehnder interferometer using single copies of the quantum state. Our result shows that for any two qubit pure bipartite state, the interference visibility is a direct measure of entanglement. We also propose how to measure the mutual predictability experimentally from the intensity patterns of the interferometric set-up without having to resort to local measurements of mutually unbiased bases. Furthermore, we show that the entanglement witness operator can be measured in an interference setup and the phase shift is sensitive to the separable or entangled nature of the state. Our proposal brings out the power of Interferometric set-up in entanglement detection of pure and several mixed states which paves the way towards design of entanglement meter.

New Journal of Physics (NJP) publishes important new research of the highest scientific quality with significance across a broad readership. The journal is owned and run by scientific societies, with the selection of content and the peer review managed by a prestigious international board of scientists.

Quantum world has several unusual features and entanglement is the most unusual feature in this wonderland. Quantum entanglement which ones thought to display spooky correlations by Einstein, has been extremely helpful as a resource in some important discoveries in quantum technology like quantum computing, quantum teleportation, quantum dense coding, quantum cryptography, remote state preparation and many other quantum communications.

However, efficient experimental certification and quantification of entanglement is still a challenging problem. There are mainly two reasons why this is demanding. Firstly, the characterization of entangled state via standard methods via quantum tomography typically requires the estimation of a large number of independent parameters, which in turn requires a large number of different measurements to be performed on the entangled system . Furthermore, even with full knowledge of the state obtained from tomography, the computational complexity of evaluating any entanglement measure increases so rapidly with increasing dimension making it a NP-hard problem. Secondly, the types of measurements that can actually be performed in a real experiment are typically limited.

The recent work by Kanjilal, Pandey and Pati proposes a method that use copies of single instances of state and a single oracle operation to determine whether the bipartite state is entangled or not. The new method is novel as one can estimate the entanglement directly from the visibility in interference setup.

These findings can pave the way towards design of an entanglement meter where we can havea portable device inside which we have the Mach–Zehnder interferometer with suitable oracles in place. By sending single copy of the local system or joint system at the input port of the entanglement meter, we can directly measure the entanglement between the pairs of subsystems. This can have several industrial applications in quantum technology. For example, if a private company is supplying maximally entangled pairs, then to convince a buyer, company can give one of the pair to the user along with the entanglement meter which has the sequence of unitaries along with the oracle. Using the entanglement meter, the end user can verify that indeed the supplied pair is maximally entangled state.

Given the importance of quantum computing and quantum technology the proposal to design entanglement meter is very timely and can have immense applications in future tech industry.

April 2023