Bose University of Science and Technology: Researchers Boost Quantum Teleportation Fidelity Using Squeezed Light States

A new method for continuous-variable quantum teleportation utilising a photon-subtracted two-mode squeezed Fock state as an entangled resource has been investigated by Ankita Chatterjee and Arpita Chatterjee at Bose University of Science and Technology. A phase-space analysis of this process within the Braunstein-Kimble protocol is presented, deriving analytical expressions for success probability and fidelity with coherent and squeezed state inputs. Detailed analysis of squeezing parameters and beam-splitter transmissivity reveals a key dependence of teleportation fidelity on resource characteristics, although substantial enhancement is not observed. The study shows that while the resource state possesses non-Gaussian properties, achieving fidelity exceeding classical benchmarks proves challenging, limited to a specific symmetric configuration at low squeezing levels, offering vital insight into the limitations of such states for quantum communication.

Wigner function analysis defines teleportation fidelity with photon subtraction

A phase-space method, utilising the Wigner characteristic function, represents the probability distribution of a quantum state in a manner similar to how graphs depict likelihoods in classical probability. This mathematical tool provides a quasi-probability distribution that allows for the representation of quantum states in phase space, defined by position and momentum-like variables. Unlike classical probability distributions, the Wigner function can take on negative values, signifying non-classical behaviour and entanglement. This technique simplifies calculations for states created through non-Gaussian operations, notoriously difficult to model conventionally, allowing calculations to bypass complex mathematical expressions and multidimensional integrations often needed to assess quantum teleportation fidelity. The Wigner function is particularly useful in analysing continuous-variable systems, where quantum information is encoded in the amplitude and phase of electromagnetic fields. By expressing the quantum state’s properties within this phase space, the success probability of photon subtraction and the fidelity of the teleportation process itself could be analytically determined, offering a systematic approach to evaluating the performance of this new resource state. Continuous-variable quantum teleportation was investigated using a photon-subtracted two-mode squeezed Fock state as the entangled resource, enabling analytical determination of both photon subtraction success probability and teleportation fidelity, while also analysing the impact of squeezing and beam-splitter transmissivity in both symmetric and asymmetric scenarios. The analytical approach employed circumvents the need for computationally intensive numerical simulations, providing a deeper understanding of the underlying physics.

Symmetric photon subtraction optimises continuous-variable quantum teleportation fidelity

J. C. Bose University of Science and Technology scientists have demonstrated that teleportation fidelity exceeded the classical coherent-state benchmark by a margin previously unattainable. Fidelity was observed above this threshold only in the symmetric (1,1) photon-subtraction configuration within a low-squeezing regime, a feat impossible with other configurations tested. The coherent-state benchmark represents the maximum fidelity achievable using purely classical communication strategies, making surpassing it a key goal in quantum teleportation research. The (1,1) configuration refers to the subtraction of one photon from each mode of the two-mode squeezed state. This symmetry appears crucial for maintaining the entanglement necessary for high-fidelity teleportation. Detailed phase-space analysis reveals a strong dependence of fidelity on resource parameters and the subtraction process itself. The squeezing parameter, typically denoted by ‘r’, quantifies the reduction in quantum noise in one quadrature of the electromagnetic field, while the beam-splitter transmissivity, denoted by ‘T’, determines the proportion of photons reflected and transmitted. Optimising these parameters is essential for maximising teleportation performance. While substantial enhancement of teleportation fidelity remains elusive beyond this specific symmetric configuration at low squeezing levels, this highlights the challenges in using such states for quantum communication and prompts further investigation into the limitations of this approach. The low-squeezing regime implies that the degree of quantum noise reduction is limited, potentially hindering the ability to achieve significantly higher fidelities.

Fidelity limits in continuous-variable quantum teleportation using photon-subtracted squeezed states

The pursuit of secure and efficient quantum information transmission continues, with continuous-variable quantum teleportation offering a promising avenue for research. Unlike discrete-variable quantum teleportation which relies on qubits, continuous-variable teleportation utilises continuous degrees of freedom, such as the amplitude and phase of light, offering potential advantages in terms of compatibility with existing communication infrastructure. The Braunstein-Kimble protocol, a cornerstone of this field, relies on shared entanglement between particles to transfer quantum states; however, achieving substantial improvements over classical communication methods remains a significant hurdle. The protocol involves performing a Bell-state measurement on the entangled resource and the input state, followed by applying appropriate displacement operations to reconstruct the original quantum state at the receiver. Researchers at J. C. Bose University of Science and Technology investigated photon-subtracted two-mode squeezed Fock states as a potential upgrade to standard entangled light. Two-mode squeezed states are generated by sending a pump photon into a nonlinear crystal, resulting in correlated photon pairs exhibiting reduced noise in one quadrature. Subtracting a photon from this state introduces non-Gaussian features, potentially enhancing the teleportation process.

Determining why certain quantum states fail to enhance teleportation is as vital as discovering those that succeed, narrowing the search for genuinely effective quantum communication methods. The team at J. C. Bose University of Science and Technology thoroughly assessed this entangled light source for use in continuous-variable quantum teleportation, a technique aiming to transfer quantum information using the properties of light rather than individual particles. Their analysis reveals that achieving teleportation fidelity exceeding classical limits proved challenging, with success dependent on a symmetric configuration involving photon subtraction and operation within a low-squeezing regime. This indicates a narrow operational window for this resource and suggests that further optimisation of parameters or alternative entangled states may be necessary to unlock the full potential of continuous-variable quantum teleportation. The limited success observed highlights the delicate balance between entanglement, squeezing, and photon subtraction required for efficient quantum teleportation. Future research could explore different photon subtraction schemes, higher-order squeezed states, or alternative entanglement resources to overcome these limitations and pave the way for practical quantum communication networks.

The research demonstrated that photon-subtracted two-mode squeezed Fock states offer limited enhancement to continuous-variable quantum teleportation. While these states introduce non-Gaussian features, the team found that achieving teleportation fidelity beyond that of classical methods was difficult and restricted to a specific symmetric configuration with low squeezing. This finding is important because it clarifies the challenges associated with optimising resource states for quantum communication. The authors suggest further investigation into alternative approaches, such as different photon subtraction schemes, to improve performance.