arXiv subjects

Aditi Sen De

Publications and source records attributed to Aditi Sen De.

At least 55 records · Page 3Linked to original sources

arXiv2025

Indefinite Time Directed Quantum Metrology

We explore the performance of the metrology scheme by employing a quantum time flip during encoding, a specific case of processes with indefinite time direction, which we refer to as indefinite time directed metrology (ITDM). In the case of single parameter estimation of a unitary, we demonstrate that our protocol can achieve Heisenberg scaling (1/N) with product probe states, surpassing the standard quantum limit (1/\sqrt{N}), where N is the number of particles in the probe. We establish this by computing the quantum Fisher information (QFI) which is a lower bound on the root mean square error occurred during parameter estimation. Although we analytically prove the optimality of the symmetric product probe state in ITDM, entangled probe states produce a higher QFI than optimal product probes without enhancing scaling, highlighting the non-essentiality of entanglement. For phase estimation, we propose a single-qubit measurement on the control qubit that accomplishes near-optimal Fisher information and eventually reaches Heisenberg scaling. Our findings reveal the best orientation of product probe states in every pertinent situation, emphasizing its independence from the parameter to be estimated in the limiting case. Furthermore, we illustrate the benefits of ITDM in noisy metrology, outperforming existing techniques in some situations.

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arXiv2025

Recovery of resources through sequential noisy measurements

Noisy unsharp measurements incorporated in quantum information protocols may hinder performance, reducing the quantum advantage. However, we show that, unlike projective measurements which completely destroy quantum correlations between nodes in quantum networks, sequential applications of noisy measurements can mitigate the adverse impact of noise in the measurement device on quantum information processing tasks. We demonstrate this in the case of concentrating entanglement on chosen nodes in quantum networks via noisy measurements performed by assisting qubits. In the case of networks with a cluster of three or higher number of qubits, we exhibit that sequentially performing optimal unsharp measurements on the assisting qubits yields localizable entanglement between two nodes akin to that obtained by optimal projective measurements on the same assisting qubits. Furthermore, we find that the proposed approach using consecutive noisy measurements can potentially be used to prepare desired states that are resource for specific quantum schemes. We also argue that assisting qubits have greater control over the qubits on which entanglement is concentrated via unsharp measurements, in contrast to sharp measurement-based protocols, which may have implications for secure quantum communication.

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arXiv2025

Quantum-enhanced sensing with variable-range interactions

The typical bound on parameter estimation, known as the standard quantum limit (SQL), can be surpassed by exploiting quantum resources such as entanglement. To estimate the magnetic probe field, we propose a quantum sensor based on a variable-range many-body quantum spin chain with a moderate transverse magnetic field. We report the threefold benefits of employing a long-range system as a quantum sensor. First, sensors with quasi-long-range interactions can always beat the SQL for all values of the coordination number, while a sensor with long-range interactions does not have this ubiquitous quantum advantage. Second, a long-range Hamiltonian outperforms a nearest-neighbor (NN) Hamiltonian in terms of both estimating precision and system-size scaling. Finally, we observe that the system with long-range interactions can go below the SQL in the presence of a high temperature of the initial state, while sensors having NN interactions cannot. Furthermore, a sensor based on the long-range Ising Hamiltonian proves to be robust against impurities in the magnetic field and when the time-inhomogeneous dephasing noise acts during interaction of the probe with the system.

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arXiv2025

Perfect transfer of arbitrary continuous variable states across optical waveguide lattices

We demonstrate that perfect state transfer can be achieved in an optical waveguide lattice governed by a Hamiltonian with modulated nearest-neighbor couplings. In particular, we report the condition that the evolution Hamiltonian should satisfy to achieve perfect transfer of any continuous variable input state. The states that can be transmitted need not have any specific properties - they may be pure or mixed, Gaussian or non-Gaussian in character, and comprise an arbitrary number of modes. We illustrate that the proposed protocol is scalable to two- and three-dimensional waveguide geometries. With the help of local phase gates on all the modes, our results can also be applied to realize a SWAP gate between mirror-symmetric modes about the center of the waveguide setup.

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arXiv2025

Coherence measure of ensembles with nonlocality without entanglement

Irreversibility between preparation and discrimination processes is manifested in the indistinguishability of orthogonal product states via local operations and classical communication (LOCC). Characterizing quantum properties for sets of states according to their local distinguishing property is one of the avenues to explain the surprising results obtained in the LOCC indistinguishability domain. We propose a measure based on the $l_1$ norm of coherence to quantitatively assess the quantumness of ensembles composed of orthogonal product states. Furthermore, to establish a hierarchy among different product ensembles, we establish a relationship between the coherence-based measure of an ensemble and the optimal success probability of distinguishing states within the ensemble using LOCC, constrained by a limited amount of classical communication and projective measurements, in the framework of minimum error state discrimination.

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arXiv2025

Measurement-based quantum computation with variable-range interacting systems

We demonstrate that weighted graph states (WGS) generated via variable-range interacting Ising spin systems where the interaction strength decays with distance as a power law, characterized by the fall-off rate, can successfully implement single- and two-qubit gates with fidelity exceeding classical limits by performing suitable measurements. In the regime of truly long-range interactions (small fall-off rate), optimizing over local unitary operations, while retaining the local measurement scheme in the original measurement-based quantum computation (MBQC) set-up, enables the scheme to achieve nonclassical average fidelities. Specifically, we identify a threshold fall-off rate of the interaction above which the fidelity of both universal single- and two-qubit gates consistently exceeds $90\%$ accuracy. Moreover, we exhibit that the gate-implementation protocol remains robust under two realistic imperfections -- noise in the measurement process, modeled via unsharp measurements, and disorder in the interaction strengths. These findings confirm WGS produced through long-range systems as a resilient and effective resource for MBQC.

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arXiv2025

Disparity between multipartite entangling and disentangling powers of unitaries: Even vs Odd

We compare the multipartite entangling and disentangling powers of unitary operators by assessing their ability to generate or eliminate genuine multipartite entanglement. Our findings reveal that while diagonal unitary operators can exhibit equal entangling and disentangling powers, certain non-diagonal unitaries demonstrate an imbalance when acting on fully separable states, thereby extending the known disparity from bipartite systems to those with any number of parties. Counterintuitively, we construct classes of unitaries and their adjoints that display unequal entanglement generation capacities, behaving differently when applied to systems with an even number of qubits compared to those with an odd number. Further, we illustrate that this asymmetry can be simulated using physically realizable Hamiltonians: systems with an even number of qubits employ nearest-neighbor Dzyaloshinskii-Moriya (DM) interactions, while those with an odd number utilize a combination of Heisenberg and DM interactions. Additionally, we present a circuit composed of random noncommuting unitaries, constructed from alternating layers of two-qubit Haar-random gates, to illustrate the discrepancy in the entangling and disentangling capabilities of unitaries.

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arXiv2025

Sequential information theoretic protocols in continuous variable systems

In order to enable the sequential implementation of quantum information theoretic protocols in the continuous variable framework, we propose two schemes for resource reusability, resource-splitting protocol and unsharp homodyne measurements. We demonstrate the advantage offered by the first scheme in implementing sequential attempts at continuous variable teleportation when the protocol fails in the previous round. In the second scheme, unsharp quadrature measurements are employed to implement the detection of entanglement between several pairs of observers. Under specific conditions, our calculations show that it is possible to successfully witness the entanglement of the same two-mode state, sequentially by as many as five observers.

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arXiv2025

Slow decay rate of correlations induced by long-range extended Dzyaloshinskii-Moriya interactions

We examine the impact of long-range Dzyaloshinskii-Moriya (DM) interaction in the extended $XY$ model on the phase diagram as well as the static and dynamical properties of quantum and classical correlation functions. It is known that in the nearest-neighbor $XY$ model with DM interaction, the transition from the gapless chiral phase to a gapped one occurs when the strengths of the DM interaction and anisotropy coincide. We exhibit that the critical line gets modified with the range of interactions which decay according to power-law. Specifically, instead of being gapless in the presence of a strong DM interaction, a gapped region emerges which grows with the increase of the moderate fall-off rate (quasi-long range regime) in the presence of a transverse magnetic field. The gapless chiral phase can also be separated from a gapped one by the decay patterns of quantum mutual information and classical correlation with distant sites of the ground state which are independent of the fall-off rate in the gapless zone. We observe that the corresponding critical lines that depend on the fall-off rate can also be determined from the effective central charge involved in the scaling of entanglement entropy. We illustrate that in a non-equilibrium setting, the relaxation dynamics of classical correlation, the decay rate of total correlation, and the growth rate of entanglement entropy can be employed to uncover whether the evolving Hamiltonian and the Hamiltonian corresponding to the initial state are gapped or gapless.

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arXiv2025

Floquet driven long-range interactions induce super-extensive scaling in quantum batteries

Achieving quantum advantage in energy storage and power extraction is a primary objective in the design of quantum-based batteries. We explore how long-range (LR) interactions in conjunction with Floquet driving can improve the performance of quantum batteries, particularly when the battery is initialized in a fully polarized state. In particular, we analytically prove that the upper bound of the instantaneous power obtained through this system-charger duo scales quadratically with moderate system-size. By optimizing the driving frequency, we demonstrate that the maximum average power which is a lower bound of the instantaneous power can achieve the super-extensive scaling with system-size, thereby providing genuine quantum advantage. Further, we illustrate that the inclusion of either two-body or many-body interaction terms in the LR charging Hamiltonian leads to a scaling benefit. We also discover that a super-linear scaling in power results from increasing the strength of interaction compared to the transverse magnetic field and the range of interaction with low fall-off rate, highlighting the advantageous role of long-range interactions in optimizing quantum battery charging.

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arXiv2025

Critical quantum metrology using non-Hermitian spin model with RT-symmetry

The non-Hermitian transverse $XY$ model with Kaplan-Shekhtman-Entin-Wohlman-Aharony (KSEA) interaction having $\mathcal{RT}$-symmetry, referred to as $iKSEA$ model, possesses both an exceptional point at which eigenvectors coalesce and a quantum critical point where gap-closing occurs. To precisely estimate the magnetic field of the system, we prove that the quantum Fisher information (QFI) of the ground state of the $iKSEA$ model, which is a lower bound of the precision quantified by the root mean square error, scales as $N^2$, with $N$ being the system-size. This provides Heisenberg scaling both at the quantum critical point and the exceptional point in the thermodynamic limit. It indicates that reservoir engineering can provide enhanced precision of system parameters when the system is in contact with the bath, resulting in this non-Hermitian model. Additionally, we demonstrate analytically that, in contrast to Hermitian systems, QFI surpasses the Heisenberg limit and achieves super-Heisenberg scaling ($\sim N^6$), when the strength of the KSEA interaction approaches the anisotropy parameter, permitting competition between non-hermiticity and hermiticity features, as long as the system size is moderate. Moreover, we illustrate that starting from a product state, the non-Hermitian evolving Hamiltonian can create the dynamical state that surpasses the standard quantum limit in the broken regime.

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arXiv2025

Tradeoff between noise and banding in a quantum adder with qudits

Quantum addition based on the quantum Fourier transform can be an integral part of a quantum circuit and proved to be more efficient than the existing classical ripple carry adder. Our study includes identifying the quantum resource required in a quantum adder in any arbitrary dimension and its relationship with the performance indicator in the presence of local noise acting on the circuit and when a limited number of controlled rotation operations is permitted, a procedure known as banding. We analytically prove an upper bound on the number of the controlled rotation gates required to accomplish the quantum addition up to an arbitrary defect in the fidelity between the desired and imperfect output. When the environment interacts with individual qudits, we establish a connection between quantum coherence and fidelity of the output. Interestingly, we demonstrate that when banding is employed in the presence of noise, approximate circuits of constant depth outperform circuits with a higher number of controlled rotations, establishing a complementary relationship between the approximate quantum adder and the strength of the noise. We exhibit that utilizing magnetic fields to prepare an initial state that evolves according to a one-dimensional spin chain for a specific amount of time can be a potential technique to implement quantum addition circuits in many-body systems.

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arXiv2025

Predicting topological quantum phase transition from dynamics via multisite entanglement

An exactly solvable Kitaev model in a two-dimensional square lattice exhibits a topological quantum phase transition which is different from the symmetry-breaking transition at zero temperature. When the ground state of a nonlinearly perturbed Kitaev model with different strengths of perturbation taken as the initial state is quenched to a pure Kitaev model, we demonstrate that various features of the dynamical state, such as the Loschmidt echo and time-averaged multipartite entanglement, can determine whether the initial state belongs to the topological phase or not. Moreover, the derivatives of the dynamical quantifiers can faithfully identify the topological quantum phase transition, which is present at equilibrium. When the individual qubits of the lattice interact with the local thermal bath repeatedly, we observe that block entanglement in dissipative dynamics can nevertheless distinguish the equilibrium phases from which the system starts evolution.

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arXiv2025

Hybrid nonlocality via atom photon interactions with and without impurities

To obtain Bell statistics from hybrid systems composed of finite- and infinite-dimensional systems, we propose a hybrid measurement scheme, in which the continuous mode is measured using the generalized pseudospin operators, while the finite (two)-dimensional system is measured in the usual Pauli basis. Maximizing the Bell expression with these hybrid measurement settings leads to the violations of local realism in hybrid system which is referred to as hybrid nonlocality. We demonstrate the utility of our strategy in a realistic setting of cavity quantum electrodynamics, where an atom interacts resonantly with a single mode of an electromagnetic field under the Jaynes-Cummings Hamiltonian. We dynamically compute the quenched averaged value of hybrid nonlocality in imperfect situations by incorporating disorder in the atom-cavity coupling strength. In the disordered case, we introduce two kinds of measurement scenarios to determine the Bell statistics -- in one situation, experimentalists can tune the optimal settings according to the interaction strength while such controlled power is absent in the other case. In contrast to the oscillatory behavior observed in the ordered case, the quenched averaged violation saturates to a finite value in some parameter regimes in the former case. We also examine the connection between Wigner negativity and hybrid nonlocality.

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arXiv2025

Developing universal logical state-purification strategy for quantum error correcting codes

We develop a measurement-based protocol for simultaneously purifying arbitrary logical states in multiple quantum error correcting codes with unit fidelity and finite probability, starting from arbitrary thermal states of each code. The protocol entails a time evolution caused by an engineered Hamiltonian, which results in transitions between the logical and error subspaces of the quantum error correcting code mediated by the auxiliary qubit, followed by a projective measurement in an optimum basis on the auxiliary qubit and an appropriate post-selection of the measurement outcomes. We illustrate the results with the three-qubit repetition code and the logical qubit used in quantum state transfer protocol. We further demonstrate that when the measurement base is not optimal, it is possible to achieve both classical fidelity, and fidelity as high as $90\%$ through several iterations of the purifying procedure, thereby establishing its robustness against variations in the measurement basis. By repeating the purification rounds, we show that purifying the cardinal states of the logical Bloch sphere corresponding to logical qubits in quantum state transfer is feasible utilizing paradigmatic quantum spin models as the generator of the time evolution.

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arXiv2025

Limits on broadcasting non-stabilizerness through unrestricted operations

In the resource theory of non-stabilizerness, we prove that stabilizer operations cannot replicate or broadcast the "magic" resource of all quantum states in an arbitrary finite dimension. Moreover, we show that even in unrestricted scenarios, there are fundamental limits on cloning the non-stabilizerness content of quantum states. When using an auxiliary system as part of the cloning process, we show that it is impossible to broadcast the non-stabilizerness of qubits that possess a greater degree of non-stabilizerness than the known states on which the transformations are based. We also derive the conditions to broadcast magic perfectly using unrestricted operations. Furthermore, we compare non-stabilizerness broadcasting with traditional state cloning methods, such as state-dependent and -independent cloners, which can achieve perfect broadcasting of states with known magic content. Our findings reveal that state-dependent cloning unitaries designed for specific states have lower average non-stabilizerness-generating power than magic-generating unitaries.

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arXiv2025

Advancing Quantum Otto Engine Performance via Additional Magnetic Field and Effective Negative Temperature

We formulate a protocol for a four-stroke quantum Otto engine that is capable of achieving superior performance when operating between two thermal reservoirs: one at a positive spin temperature and the other at an effective negative spin temperature. We adopt a protocol that encompasses a rotating magnetic field in the (x, y)-plane, as well as an additional magnetic field in the (z)-direction that possesses distinct strengths. Consequently, we acquire the capability to manipulate the strength of the magnetic field autonomously in both directions during dynamics. We report that by precisely adjusting the strength and the direction of the magnetic field in the (z)-direction and manipulating other relevant system parameters, we can effectively enhance the transition probability and hence the efficiency of the engine as well which can not be achieved without the additional magnetic field, although the impact is not ubiquitous. Additionally, another important significance of our model is that these engines operate within an extended operational domain, reaching into temperature ranges where the effective negative temperature-based quantum Otto engines operating only on the rotational magnetic field in the (x,y) plane, are unable to function. Specifically, we identify a threshold value for the magnetic field, dependent on the driving time, at which an improvement in efficiency is observed. We propose that this advantage may arise from the system exhibiting greater coherence with respect to the driving time, which we evaluate using the l1-norm coherence measure. Another noteworthy aspect is that the advantage in efficiency gained from the additional magnetic field continues to surpass that of the protocol without the field, even in the presence of impurities in the magnetic field having a specific range of disorder strengths.

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arXiv2025

Information theoretic resource-breaking channels

We propose the notion of process resource-breaking channels that break the resource for a quantum information processing task. We examine the same using quantum dense coding and teleportation protocols. We prove that the sets DBT (dense coding breaking) and TBT (teleportation breaking) are convex and compact and identify classical-quantum channels as their extreme points. We prove group-covariance to be a sufficient condition for channels to be DBT or TBT when they can destroy the resource of maximally entangled states. We present necessary and sufficient conditions for unital channels to be DBT for a single sender-receiver pair, while for multiple senders, the condition is sufficient. The set of qubit TBT channels is proved equivalent to qubit entanglement-breaking channels provided pre-processing is allowed. We construct witness operators to identify non-TBT(non-DBT) maps.

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