Quantum Teleportation Enhanced Using Superposition of Paths and Separable States

Researchers demonstrated enhanced quantum teleportation utilising superposition of processes – specifically, superposition of paths – to achieve successful state transfer even when parties share separable, including product, states. This contrasts with indefinite causal order superposition, and requires coherence in a control qubit to realise the advantage.

Quantum teleportation, a process enabling the transfer of quantum states without physical transmission of the quantum system itself, conventionally relies upon shared entanglement between distant parties. Researchers have now demonstrated a pathway to achieve perfect quantum teleportation utilising an alternative resource: the superposition of different possible processes by which information can be transferred. This approach circumvents the usual requirement for entangled states, functioning effectively even with separable, non-entangled states in certain instances. Sayan Mondal, Priya Ghosh, and Ujjwal Sen, from the Harish-Chandra Research Institute, detail their findings in the article “Path superposition as resource for perfect quantum teleportation with separable states”, published this week, where they explore the conditions under which this ‘path superposition’ enables reliable quantum communication.

Manipulating Quantum Order Enhances Information Processing and Device Functionality

Investigations consistently demonstrate that manipulating the order of quantum operations enhances quantum information processing and device functionality. This work centres on the principle of indefinite causal order, where the sequence of operations applied to a quantum system is not predetermined, and the implementation of quantum switches to control these sequences.

Quantum metrology benefits significantly from this approach. By manipulating the order of operations, researchers achieve measurement precision exceeding the standard quantum limit – a fundamental constraint imposed by conventional measurement techniques. This improvement arises because indefinite causal order allows for the creation of non-classical correlations that reduce measurement uncertainty.

A key development lies in optimising quantum communication protocols. Researchers have successfully demonstrated quantum teleportation – the transfer of a quantum state from one location to another – utilising shared, non-entangled states.  Conventional teleportation relies on pre-shared entanglement between the sender and receiver. This new approach employs a superposition of pathways, effectively circumventing the entanglement requirement and broadening the scope for quantum communication networks, particularly in scenarios where entanglement distribution is challenging.

The correlation between quantum coherence – the preservation of a quantum system’s superposition – and the observed performance gains in teleportation is strong. Experiments confirm coherence as both a necessary and sufficient condition for achieving improvements. This reinforces the understanding of coherence as a critical quantum resource and contributes to the development of a more comprehensive resource theory, allowing for a refined assessment of the capabilities offered by manipulating causal order. Maintaining coherence, however, remains a significant challenge in complex quantum systems.

Practical applications are emerging beyond fundamental studies. Researchers have experimentally realised quantum refrigerators driven by indefinite causal orders, demonstrating the feasibility of building functional quantum thermal devices. Theoretical work extends these principles to other thermal devices, suggesting pathways towards energy-efficient cooling and heating systems. Coupled with ongoing investigations into universal quantum switches – devices capable of controlling the flow of quantum information – these developments signal a transition from theoretical exploration towards tangible devices.

Future research should prioritise scaling these implementations. Addressing the challenges of maintaining coherence in increasingly complex systems is paramount. Innovative solutions for mitigating decoherence – the loss of quantum information due to interaction with the environment – and preserving the delicate quantum states necessary for these technologies are crucial. Exploring novel methods for generating and manipulating indefinite causal order, alongside developing more robust quantum switches, will be essential for advancing the field. Investigating the interplay between different types of superposition – pathways and indefinite causal order – could unlock further advantages in quantum communication and computation.