arXiv subjects

Arvind

Publications and source records attributed to Arvind.

At least 37 records · Page 2Linked to original sources

arXiv2024

Ground and excited state energy calculations of the H2 molecule using a variational quantum eigensolver algorithm on an NMR quantum simulator

Variational quantum algorithms are emerging as promising candidates for near-term practical applications of quantum information processors, in the field of quantum chemistry. We implement the variational quantum eigensolver algorithm to calculate the molecular ground-state energy of the H2 molecule and experimentally demonstrated it on an NMR quantum processor. Further, we simulate the excited states of the H2 molecule using the variational quantum deflation algorithm and experimentally demonstrate it on the same NMR quantum processor. We also develop the first simulation of the energy calculation of the H2 molecule using only a single qubit, and verify the results on an NMR quantum computer. Our experimental results demonstrate that only a single NMR qubit suffices to calculate the molecular energies of the H2 molecule to the desired accuracy.

quant-ph↗

arXiv2024

Re-examination of the role of displacement and photon catalysis operation in continuous variable measurement device-independent quantum key distribution

We investigate the benefits of using $m$-photon catalysed two-mode squeezed coherent ($m$-PCTMSC) state in continuous variable measurement device-independent quantum key distribution (CV-MDI-QKD). To that end, we derive the Wigner characteristic function of the $m$-PCTMSC state and show that the 0-PCTMSC state is a Gaussian state and is an inferior choice as compared to the zero photon catalyzed two-mode squeezed vacuum state for CV-MDI-QKD. We carry out the optimization of the secret key rate with respect to all state parameters, namely variance, transmissivity, and displacement. Contrary to many recent proposals, the results show that zero- and single-photon catalysis operation provides only a marginal benefit in improving the maximum transmission distance. Secondly, we find that displacement offers no benefit in improving CV-MDI-QKD.

quant-ph↗

arXiv2024

Optimization of state parameters in displacement assisted photon subtracted measurement-device-independent quantum key distribution

Non-Gaussian operations, in particular, photon subtraction (PS), have been shown to enhance the performance of various quantum information processing tasks including continuous variable measurement device independent quantum key distribution (CV-MDI-QKD). This work investigates the role of non-Gaussian resource states, namely, the photon subtracted two-mode squeezed coherent (PSTMSC) (which include photon subtracted two-mode squeezed vacuum (PSTMSV) as a special case) states in CV-MDI-QKD. To this end, we derive the Wigner characteristic function for the resource states, from which the covariance matrix and, finally, the secret key rate expressions are extracted. The optimization of the state parameters is undertaken to find the most suitable resource states in this family of states. There have been previous studies on the PSTMSV and PSTMSC states in CV-MDI-QKD that make use of PS operation. We evaluate such proposals and find to our surprise that both PSTMSC and PSTMSV resource states underperform as compared to the TMSV state rendering PS operation and displacement undesirable.

quant-ph↗

arXiv2024

No real advantage of photon subtraction and displacement in continuous variable measurement device independent quantum key distribution

We critically analyse the role of single photon subtraction (SPS) and displacement in improving the performance of continuous variable measurement device independent quantum key distribution (CV-MDI-QKD). We consider CV-MDI-QKD with resource states generated by SPS on a displaced two-mode squeezed vacuum state. Optimizing the secret key rate with state parameters reveals that implementing SPS yields no benefits in improving the loss tolerance of CV-MDI-QKD. Additionally, we find that displacement too is not useful in improving the performance of CV-MDI-QKD. While our result is in contradistinction with the widely held belief in the field regarding the utility of SPS and displacement in CV-MDI-QKD, it also calls for a re-examination of the role of non-Gaussian operations in increasing the efficiency of various quantum information processing protocols.

quant-ph↗

arXiv2023

Inferring physical laws by artificial intelligence based causal models

The advances in Artificial Intelligence (AI) and Machine Learning (ML) have opened up many avenues for scientific research, and are adding new dimensions to the process of knowledge creation. However, even the most powerful and versatile of ML applications till date are primarily in the domain of analysis of associations and boil down to complex data fitting. Judea Pearl has pointed out that Artificial General Intelligence must involve interventions involving the acts of doing and imagining. Any machine assisted scientific discovery thus must include casual analysis and interventions. In this context, we propose a causal learning model of physical principles, which not only recognizes correlations but also brings out casual relationships. We use the principles of causal inference and interventions to study the cause-and-effect relationships in the context of some well-known physical phenomena. We show that this technique can not only figure out associations among data, but is also able to correctly ascertain the cause-and-effect relations amongst the variables, thereby strengthening (or weakening) our confidence in the proposed model of the underlying physical process.

cs.AI↗

arXiv2023

Quantum operations restricted by no faster-than-light communication principle and generic emergence of objectivity in position basis

The emergence of the objective classical world from the quantum behavior of microscopic constituents is not fully understood. Models based on decoherence and the principle of quantum Darwinism, which attempt to provide such an explanation, require system-bath interactions in a preferred basis. Thus, the generic emergence of objectivity in the position basis, as observed in the real world remains unexplained. In this Letter, we present a no-go theorem based on the principle of no-faster-than-light communication, showing that interactions between internal degrees of freedom unavoidably cause system wave functions to branch in the position basis. We apply this result to a spin decoherence model to demonstrate that a generic thermal spin-1/2 bath redundantly records information about the position of a spin-1/2 particle. Notably, the model does not assume any preferred spin interaction. These findings represent a compelling demonstration of the generic emergence of objectivity in the position basis.

quant-ph↗

arXiv2023

Experimental quantum state transfer of an arbitrary single-qubit state on a cycle with four vertices using a coined quantum random walk

We experimentally demonstrate the transfer of an unknown single-qubit state from Alice to Bob via a two-step discrete-time quantum random walk on a cycle with four vertices on a four-qubit nuclear magnetic resonance quantum processor. The qubits with Alice and Bob are used as coin qubits and the walk is carried out on in a two-qubit `Gaming Arena'. In this scheme, the required entangled state is generated naturally via conditional shift operators during the quantum walk, instead of being prepared in advance. We implement controlled operators at Bob's end, which are controlled by Alice's coin qubit and arena qubits, in order to reconstruct Alice's randomly generated state at Bob's end. To characterize the state transfer process, we perform quantum process tomography by repeating the experiment for a set of input states $\{ \vert 0\rangle, \vert 1\rangle, \vert +\rangle, \vert -\rangle \}$. Using an entanglement witness, we certify that the quantum walk generates a genuine quadripartite entangled state of all four qubits. To evaluate the efficacy of the transfer scheme, We use quantum state tomography to reconstruct the transferred state by calculating the projection of the experimentally reconstructed four-qubit density matrix onto three-qubit basis states. Our results demonstrate that the quantum circuit is able to perform quantum state transfer via the two-step quantum random walk with high fidelity.

quant-ph↗

arXiv2023

Neural network assisted quantum state and process tomography using limited data sets

In this study we employ a feed-forward artificial neural network (FFNN) architecture to perform tomography of quantum states and processes obtained from noisy experimental data. To evaluate the performance of the FFNN, we use a heavily reduced data set and show that the density and process matrices of unknown quantum states and processes can be reconstructed with high fidelity. We use the FFNN model to tomograph 100 two-qubit and 128 three-qubit states which were experimentally generated on a nuclear magnetic resonance (NMR) quantum processor. The FFNN model is further used to characterize different quantum processes including two-qubit entangling gates, a shaped pulsed field gradient, intrinsic decoherence processes present in an NMR system, and various two-qubit noise channels (correlated bit flip, correlated phase flip and a combined bit and phase flip). The results obtained via the FFNN model are compared with standard quantum state and process tomography methods and the computed fidelities demonstrates that for all cases, the FFNN model outperforms the standard methods for tomography.

quant-ph↗

arXiv2023

State-independent robust heat-bath algorithmic cooling of nuclear spins

In this work, we experimentally demonstrate the implementation of a recently proposed robust and state-independent heat-bath algorithmic cooling (HBAC) method [1] on an NMR quantum processor. While HBAC methods improve the purity of a quantum system via iterative unitary entropy compression, they are difficult to implement experimentally since they use sort operations that are different for each iteration. The new robust HBAC method proved that optimal HBAC is possible without prior state information and using a single fixed operation. We modified the protocol to experimentally perform efficient cooling of 13C and 15N spins and provide an optimal decomposition of this modified protocol in terms of quantum gates. This is the first time that optimal HBAC has been experimentally demonstrated on 15N spins. We examined the relaxation dynamics of these algorithmically cooled spins, in order to ascertain the effect of decoherence on the cooled states.

quant-ph↗

arXiv2023

Direct tomography of quantum states and processes via weak measurements of Pauli spin operators on an NMR quantum processor

In this paper, we present an efficient weak measurement-based scheme for direct quantum state tomography (DQST) and direct quantum process tomography (DQPT), and experimentally implement it on an NMR ensemble quantum information processor without involving any projective measurements. We develop a generalized quantum circuit that enables us to directly measure selected elements of the density matrix and process matrix which characterize unknown quantum states and processes, respectively. This generalized quantum circuit uses the scalar J-coupling to control the interaction strength between the system qubits and the metre qubit. We experimentally implement these weak measurement-based DQST and DQPT protocols and use them to accurately characterize several two-qubit quantum states and single-qubit quantum processes. An extra qubit is used as a metre qubit to implement the DQST protocol, while for the DQPT protocol, two extra qubits (one as a metre qubit and the other as an ancilla qubit) are used.

quant-ph↗

arXiv2023

Revealing quantum contextuality using a single measurement device

In this work we analyse the notion of measurement non-contextuality (MNC) and identify contextual scenarios which involve sequential measurements of only a single measurement device. We show that any non-contextual ontological model fails to explain the statistics of outcomes of a single carefully constructed positive operator valued measure (POVM) executed sequentially on a quantum system. The context of measurement arises from the different configurations in which the device can be used. We develop an inequality from the non-contextual (NC) ontic model, and construct a quantum situation involving measurements from the KCBS inequality. We show that the resultant statistics arising from this device violate our NC inequality. This device can be generalised by incorporating measurements from arbitrary $n$-cycle contextuality inequalities of which $n = 5$ corresponds to the KCBS inequality. We show that the NC and quantum bounds for various scenarios can be derived more easily using only the functional relationships between the outcomes for larger values $n$. This makes it one of the simpler contextual inequalities to analyse.

quant-ph↗

arXiv2022

Efficient and Scalable Graph Pattern Mining on GPUs

Graph Pattern Mining (GPM) extracts higher-order information in a large graph by searching for small patterns of interest. GPM applications are computationally expensive, and thus attractive for GPU acceleration. Unfortunately, due to the complexity of GPM algorithms and parallel hardware, hand optimizing GPM applications suffers programming complexity, while existing GPM frameworks sacrifice efficiency for programmability. Moreover, little work has been done on GPU to scale GPM computation to large problem sizes. We describe G2Miner, the first Graph Pattern Mining (GPM) framework that runs on multiple GPUs. G2Miner uses pattern-aware, input-aware and architecture-aware search strategies to achieve high efficiency on GPUs. To simplify programming, it provides a code generator that automatically generates pattern-aware CUDA code. G2Miner flexibly supports both breadth-first search (BFS) and depth-first search (DFS) to maximize memory utilization and generate sufficient parallelism for GPUs. For the scalability of G2Miner, we use a customized scheduling policy to balance work among multiple GPUs. Experiments on a V100 GPU show that G2Miner achieves average speedups of 5.4x and 7.2x over two state-of-the-art single-GPU systems, Pangolin and PBE, respectively. In the multi-GPU setting, G2Miner achieves linear speedups from 1 to 8 GPUs, for various patterns and data graphs. We also show that G2Miner on a V100 GPU is 48.3x and 15.2x faster than the state-of-the-art CPU-based system, Peregrine and GraphZero, on a 56-core CPU machine.

cs.DC↗

arXiv2022

Experimental construction of a symmetric three-qubit entangled state and its utility in testing the violation of a Bell inequality on an NMR quantum simulator

We designed a quantum circuit to prepare a permutation-symmetric maximally entangled three-qubit state called the $\vert {\rm S} \rangle$ state and experimentally created it on an NMR quantum processor. The presence of entanglement in the state was certified by computing two different entanglement measures, namely negativity and concurrence. We used the $\vert {\rm S} \rangle$ state in conjunction with a set of maximally incompatible local measurements, to demonstrate the maximal violation of inequality number $26$ in Sliwa's classification scheme, which is a tight Bell inequality for the (3,2,2) scenario i.e. the three party, two measurement settings and two measurement outcomes scenario.

quant-ph↗

arXiv2022

Classification and measurement of multipartite entanglement by reconstruction of correlation tensors on an NMR quantum processor

We introduce a protocol to classify three-qubit pure states into different entanglement classes and implement it on an NMR quantum processor. The protocol is designed in such a way that the experiments performed to classify the states can also measure the amount of entanglement present in the state. The classification requires the experimental reconstruction of the correlation matrices using 13 operators. The rank of the correlation matrices provide the criteria to classify the state in one of the five classes, namely, separable, biseparable (of three types), and genuinely entangled (of two types, GHZ and W). To quantify the entanglement, a concurrence function is defined which measures the global entanglement present in the state, using the same 13 operators. Global entanglement is zero for separable states and non-zero otherwise. We demonstrate the efficacy of the protocol by implementing it on states chosen from each of the six inequivalent (under stochastic local operations and classical communication) classes for three qubits. We also implement the protocol on states picked at random from the state space of three-qubit pure states.

quant-ph↗

arXiv2022

No contextual advantage in non-paradoxical scenarios of two state vector formalism

The two state vector formalism (TSVF) was proposed by Aharonov, Bergmann, and Lebowitz (ABL) to provide a way for the counterfactual assignment of the probabilities of outcomes of contemplated but unperformed measurements on quantum systems. This formalism underlies various aspects of foundations of quantum theory and has been used significantly in the development of weak values and several proofs of quantum contextuality. We consider the application of TSVF, with pre- and post-selection (PPS) and the corresponding ABL rule, as a means to unearth quantum contextuality. We use the principle of exclusivity to classify the resultant pre- and post-selection scenarios as either paradoxical or non-paradoxical. In light of this, we find that several previous proofs of the emergence of contextuality in PPS scenarios are only possible if the principle of exclusivity is violated and are therefore classified as paradoxical. We argue that these do not constitute a proper test of contextuality. Furthermore, we provide a numerical analysis for the KCBS scenario as applied in the paradigm of TSVF and find that non-paradoxical scenarios do not offer any contextual advantage. Our approach can be easily generalized for other contextual scenarios as well.

quant-ph↗

arXiv2022

Evolution of two-mode quantum states under a dissipative environment: which quantum resource survives better, squeezing or entanglement?

We explore the relative robustness of squeezing and entanglement (which are quantum resources interconvertible via passive optics) for two-mode Gaussian states under different dissipative environments. When the individual modes interact with identical local baths, entanglement and squeezing decay at the same rate. However, when only one of the modes interacts with a local bath, the comparative robustness of entanglement and squeezing depends on the initial squeezing of the state. Similarly, when the system interacts with a global bath, the robustness of entanglement and squeezing depends on the initial squeezing. Thus depending on the nature of dissipative environments and the initial squeezing of the state, one can select the more robust form of resource out of squeezing and entanglement to store quantumness. This can be used to effectively enhance the performance of various quantum information processing protocols based on continuous variable Gaussian states.

quant-ph↗

arXiv2022

Simulating open quantum dynamics on an NMR quantum processor using the Sz.-Nagy dilation algorithm

We experimentally implement the Sz.-Nagy dilation algorithm to simulate open quantum dynamics on an nuclear magnetic resonance (NMR) quantum processor. The Sz.-Nagy algorithm enables the simulation of the dynamics of arbitrary-dimensional open quantum systems, using only a single ancilla qubit. We experimentally simulate the action of two non-unitary processes, namely, a phase damping channel acting independently on two qubits and a magnetic field gradient pulse (MFGP) acting on an ensemble of two coupled nuclear spin-1/2 particles. To evaluate the quality of the experimentally simulated quantum process, we perform convex optimization-based full quantum process tomography to reconstruct the quantum process from the experimental data and compare it with the target quantum process to be simulated.

quant-ph↗

arXiv2022

Generating sustained coherence in a quantum memory for retrieval at the times of quantum revival

We study the time degradation of quantum information stored in a quantum memory device under a dissipative environment in a parameter range which is experimentally relevant. The quantum memory under consideration comprises of an optomechanical system with additional Kerr non-linearity in the optical mode and an anharmonic mechanical oscillator with quadratic non-linearity. Time degradation is monitored, both in terms of loss of coherence which is analyzed with the help of Wigner functions, as well as in terms of loss of amplitude of the original state studied as a function of time. While our time trajectories explore the degree to which the stored information degrades depending upon the variation in values of various parameters involved, we suggest a set of parameters for which the original information can be retrieved without degradation. We come across a highly attention seeking situation where the role played by the non-linearity is insignificant and the system behaves as if the information is stored in a linear medium. For this case, the information retrieval is independent of the coherence revival time and can be retrieved at any instant during the time evolution.

quant-ph↗