Abstract The warehouse layout problem (WLP), also known as warehouse slotting problem, aims to determine the assignment of products to storage locations while minimizing the total travel distance for picking operations. It is combinatorial in nature and well-known to be NP-hard. To obtain high-quality solutions to medium and large WLP instances efficiently remains a computational challenge, which has motivated our work on applying quantum optimization algorithms for this problem. We reformulate the classical quadratic assignment programming (QAP) model of the WLP to a quadratic unconstrained binary optimization (QUBO) model. Our QUBO model avoids adding slack variables and reduces additional overheads as in the typical QUBO reformulation approach, which facilitates the application of the D-Wave Leap Hybrid solver. Computational study is performed on a use case with 30 stock-keeping-units (SKUs) and 32 storage slots, for which the QUBO formulation has 960 binary decision variables. We show that the D-Wave Leap Hybrid solver finds better solution to the base scenario than the exact IBM CPLEX mixed-integer quadratic programming (MIQP) solver operating under a 60-second wall-clock limit, one-tenth of the 600-second budget allocated to CPLEX in this experimental design. A sensitivity analysis across 30 scenarios, generated by crossing five annual pick volume profiles with six co-picking matrix density levels (0.5 to 1.0), shows that the D-Wave hybrid solver outperforms CPLEX MIQP solver in 26 of 30 cases, with solution quality improvements of 0.4 to 12.1%. D-Wave’s advantage generally increases as the density of co-picking matrix decreases. These results demonstrate quantum utility for WLP and motivate further investigation of hybrid quantum-classical methods for combinatorial logistics optimization at industrial strength scales.
Abstract The warehouse layout problem (WLP), also known as warehouse slotting problem, aims to determine the assignment of products to storage locations while minimizing the total travel distance for picking operations. It is combinatorial in nature and well-known to be NP-hard. To obtain high-quality solutions to medium and large WLP instances efficiently remains a computational challenge, which has motivated our work on applying quantum optimization algorithms for this problem. We reformulate the classical quadratic assignment programming (QAP) model of the WLP to a quadratic unconstrained binary optimization (QUBO) model. Our QUBO model avoids adding slack variables and reduces additional overheads as in the typical QUBO reformulation approach, which facilitates the application of the D-Wave Leap Hybrid solver. Computational study is performed on a use case with 30 stock-keeping-units (SKUs) and 32 storage slots, for which the QUBO formulation has 960 binary decision variables. We show that the D-Wave Leap Hybrid solver finds better solution to the base scenario than the exact IBM CPLEX mixed-integer quadratic programming (MIQP) solver operating under a 60-second wall-clock limit, one-tenth of the 600-second budget allocated to CPLEX in this experimental design. A sensitivity analysis across 30 scenarios, generated by crossing five annual pick volume profiles with six co-picking matrix density levels (0.5 to 1.0), shows that the D-Wave hybrid solver outperforms CPLEX MIQP solver in 26 of 30 cases, with solution quality improvements of 0.4 to 12.1%. D-Wave’s advantage generally increases as the density of co-picking matrix decreases. These results demonstrate quantum utility for WLP and motivate further investigation of hybrid quantum-classical methods for combinatorial logistics optimization at industrial strength scales.
This study compares the performance of D-Wave’s two quantum-classical hybrid optimization solvers, which integrate quantum computing principles with classical optimization techniques to solve complex optimization problems. It focuses on the Binary Quadratic Model (BQM) solver, which encodes optimization problems using a binary quadratic formulation, and the Constrained Quadratic Model (CQM) solver, which can incorporate constraints into the model. The solvers were tested on five combinatorial optimization problems: Traveling Salesman Problem (TSP), Quadratic Knapsack Problem (QKP), Quadratic Assignment Problem (QAP), Weighted Max-Cut Problem (WMP), and Maximum Clique Problem (MCP). The goal is to quantify the accuracy of solutions compared to the optimal ones. Experiments on multiple instances with known optimal solutions examined solver behavior and solution quality. At default execution durations, the CQM solver generally outperforms BQM with lower error and higher consistency. Across all test problem instances in TSP, QKP, QAP, and WMP, the CQM solver achieved lower average absolute errors by 48.38, 27.83, 21.29, and 0.05 percentage points, respectively, compared to the BQM solver. An exception was found in MCP, where the BQM solver outperformed the CQM solver by 0.75 percentage points. These findings provide a guide for end users to understand the characteristics of the solvers and to select the appropriate solver for their specific optimization problems.
Quadratic unconstrained binary optimization problems (QUBOs) are intensively discussed in the realm of quantum computing and polynomial optimization. We provide a vast experimental study of semidefinite programming (SDP) relaxations of QUBOs using sums of squares methods and on Hamiltonian Updates. We test on QUBO reformulations of industry-based instances of the (open) vehicle routing problem and the (affinity-based) slotting problem -- two common combinatorial optimization problems in logistics. Beyond comparing the performance of various methods and software, our results reaffirm that optimizing over non-generic, real-world instances provides additional challenges. In consequence, this study underscores recent developments towards structure exploitation and specialized solver development for the used methods and simultaneously shows that further research is necessary in this direction both on the classical and the quantum side.
This paper addresses the Pickup and Delivery Problem with Time Windows (PDPTW), an NP-hard combinatorial optimization problem with major practical relevance in logistics and transportation. The study focuses on a quadratic unconstrained binary optimization (QUBO) formulation for quantum annealing and benchmarks it against two classical optimization paradigms. A modular Python framework is developed that encodes PDPTW in three ways: a mixed-integer linear programming (MILP) model that serves as an exact reference, a genetic algorithm (GA) metaheuristic, and a QUBO model that is compatible with quantum annealers. The framework supports test scenarios with increasing structural complexity, with both feasible and intentionally infeasible instances. An additional contribution is the conceptual design and preliminary analysis of an automatic-penalty weight-tuning scheme for the QUBO model. Experimental results show that the proposed QUBO formulation can produce high-quality solutions for simpler PDPTW instances, but its performance strongly depends on the careful calibration of penalty weights. MILP provides optimal baselines on small instances but becomes intractable as problem size grows. The GA scales to the largest scenario and finds feasible solutions of reasonable quality, but they are not necessarily optimal. The evaluation also includes a large number of problem instances and runs on IBM Quantum hardware using the Quantum Approximate Optimization Algorithm (QAOA).
E-commerce platforms face ever more complex dimensional SKU portfolios, demand volatility, returns, seasonality and cost pressures. Traditional optimization approaches (integer programming, heuristics, meta-heuristics) increasingly strain under scale, real-time demands and combinatorial explosion. Meanwhile, quantum-inspired optimization leveraging methods such as quantum annealing, coherent Ising machines, variational circuits and QUBO (Quadratic Unconstrained Binary Optimization) mapping offer near-term practical approaches to combinatorial logistics and inventory problems. This paper proposes a comprehensive framework for applying quantum-inspired optimization to e-commerce supply-chain logistics and inventory management: we provide an extended literature review of classical and quantum-inspired methods; we derive full mathematical formulations for logistics/inventory problems and map them into QUBO/quantum-inspired frameworks; we design a benchmarking/implementation methodology; we discuss industry architecture and deployment issues (data pipelines, latency, hybrid classical/quantum-inspired workflows, interpretability, cost benefit); we present use cases and discuss practical adoption in ecommerce. Our findings suggest that while fully fault-tolerant quantum computing remains some years away, quantum-inspired optimization can deliver meaningful improvements in logistics and inventory decisions today, particularly for large-SKU e-commerce, multi-warehouse networks and time-sensitive delivery.
The optimization of front-end crude oil scheduling is a critical determinant of refinery profitability and operational stability. However, the coupling of discrete logistics events (e.g., vessel berthing) with continuous material flows (e.g., pipeline transfers) renders this problem an NP-hard Mixed-Integer Linear Programming (MILP) challenge, often intractable for classical solvers at industrial scales. This study proposes a novel hybrid quantum-classical framework to address these computational bottlenecks. We employ Benders Decomposition to decouple the monolithic model into a discrete Master Problem (MP) and a continuous Subproblem (SP). To exploit the search capabilities of quantum computing, the MP is reformulated as a Quadratic Unconstrained Binary Optimization (QUBO) model and solved via a hybrid quantum solver, while the SP enforces mass balance and quality constraints through iterative optimality and feasibility cuts. Extensive experiments on 15 multi-scale instances demonstrate that the proposed framework significantly outperforms traditional metaheuristics (e.g., Genetic Algorithms, Tabu Search), reducing total operating costs by approximately 73--80% and achieving computational speeds comparable to state-of-the-art commercial solvers (Gurobi). By effectively leveraging global optimality cuts, the method overcomes the tendency of heuristic approaches to trap in local optima, providing a robust and scalable solution for complex refinery logistics.
Abstract Quantum computers have strict requirements for the problems that they can efficiently solve. One of the principal limiting factor for the performances of noisy intermediate-scale quantum (NISQ) devices is the number of qubits required by the running algorithm. Several combinatorial optimization problems can be solved with NISQ devices once that a corresponding quadratic unconstrained binary optimization (QUBO) form is derived. Numerous techniques have been proposed to achieve such reformulations and, depending on the method chosen, the number of binary variables required, and therefore of qubits, can vary considerably. The aim of this work is to drastically reduce the variables needed for these QUBO reformulations in order to unlock the possibility to efficiently obtain optimal solutions for a class of optimization problems with NISQ devices. This goal is achieved by introducing novel tools that allow an efficient use of slack variables, even for problems with non-linear constraints, without the need to approximate the starting problem. We divide our new techniques in two independent parts, called the iterative quadratic polynomial and the master-satellite methods. Hence, we show how to apply our techniques in case of an NP-hard optimization problem inspired by a real-world financial scenario called Max-Profit Balance Settlement . We follow by submitting several instances of this problem to two D-wave quantum annealers, comparing the performances of our novel approach with the standard methods used in these scenarios. Moreover, this study allows to appreciate several performance differences between the D-wave Advantage and next-generation Advantage2 quantum annealers. We show that the adoption of our techniques in this context allows to obtain QUBO formulations with significantly fewer slack variables, i.e. around 90% less, and D-wave annealers provide considerably higher correct solution rates, which moreover do not decrease with the input size as fast as when adopting standard techniques.